That wouldn't work on most Linux distros, and the installed Qt would need to exactly match the verison of Qt I built my application with.

An exact match is not needed. Qt promises compatibility: If you build your application with an older version of Qt 6, then users can run it with a newer version of Qt 6.

There have been times when compatibility was accidentally broken. When this happens, it is treated as a critical bug and all effort will be made to restore compatibility (example: https://qt-project.atlassian.net/browse/QTBUG-135578 )

Anyway, building and shipping libqtlxqt.so remains a valid solution.

Alternatively, you could make your application depend on the distro's copy of Qt

That wouldn't work on most Linux distros, and the installed Qt would need to exactly match the verison of Qt I built my application with.

I should build and ship them with my product??

It looks like you already ship a copy of Qt and its official plugins. So, it makes sense to ship a copy of the 3rd-party plugin of interest too, right? @IgKh already found the source code for you in an earlier post, which contains compilation instructions.: https://github.com/lxqt/lxqt-qtplugin

Alternatively, you could make your application depend on the distro's copy of Qt instead of your own copy. That way, the app can also load the distro's copy of libqtlxqt.so

The only way that makes sense to me is for Qt to ship them.

Again: it's a third party plugin. How can Qt ship this at all? Ask your distribution to ship it as this is the right place.

The only way that makes sense to me is for Qt to ship them.

As things stand, the theme support just doesn’t work for any Lubuntu users.

D.

You need to build that plug-in with the Qt version you use to build your application. What happens is that you have Qt 6.10.0 loaded in memory for your application but that plug-in was built for 6.10.2.

I then tried export QT_QPA_PLATFORMTHEME=lxqt and got:

qt.core.plugin.factoryloader: looking at "libqtlxqt.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/platformthemes/libqtlxqt.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformThemeFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "lxqt"
        ]
    },
    "archlevel": 1,
    "className": "LXQtPlatformThemePlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("lxqt")
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/platformthemes" ...
qt.core.library: "/opt/DeepSkyStacker/plugins/platformthemes/libqtlxqt.so" cannot load: Cannot load library /opt/DeepSkyStacker/plugins/platformthemes/libqtlxqt.so: /usr/lib/x86_64-linux-gnu/libQt6Svg.so.6: undefined symbol: _ZN14QObjectPrivateC2E16QtPrivate_6_10_2, version Qt_6_PRIVATE_API
qt.core.plugin.loader: QLibraryPrivate::loadPlugin failed on "/opt/DeepSkyStacker/plugins/platformthemes/libqtlxqt.so" : "Cannot load library /opt/DeepSkyStacker/plugins/platformthemes/libqtlxqt.so: /usr/lib/x86_64-linux-gnu/libQt6Svg.so.6: undefined symbol: _ZN14QObjectPrivateC2E16QtPrivate_6_10_2, version Qt_6_PRIVATE_API"

so this is definitely above my salary level :(

David

But my install takes the theme plugins from /opt/DeepSkyStacker/plugins/platforms/platformthemes which contains plugins that were copied from /opt/Qt/6.10.0/gcc_64/plugins/platformthemes on my build system which doesn't include the lxqt plugin.

As lxqt does ship a suitable plugin, how can this be included as part of the Qt6 distribution for Linux (not the one that comes with the system as I have no control over the level of that!).

Looks like the QT distribution should also add a plugins/styles containing at least the Breeze and Kvantum plugins as shown here from the startup of an lxqt aware qt app (the desktop) on the system:

Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.factoryloader: checking directory path "/usr/lib/x86_64-linux-gnu/qt6/plugins/styles" ...
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.factoryloader: looking at "breeze6.so"
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.loader: Found metadata in lib /usr/lib/x86_64-linux-gnu/qt6/plugins/styles/breeze6.so, metadata=
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: {
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "IID": "org.qt-project.Qt.QStyleFactoryInterface",
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "MetaData": {
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:         "Keys": [
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:             "Breeze"
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:         ]
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     },
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "archlevel": 1,
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "className": "StylePlugin",
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "debug": false,
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "version": 395776
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: }
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.factoryloader: Got keys from plugin meta data QList("breeze")
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.factoryloader: looking at "libkvantum.so"
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.loader: Found metadata in lib /usr/lib/x86_64-linux-gnu/qt6/plugins/styles/libkvantum.so, metadata=
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: {
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "IID": "org.qt-project.Qt.QStyleFactoryInterface",
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "MetaData": {
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:         "Keys": [
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:             "kvantum",
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:             "kvantum-dark"
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:         ]
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     },
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "archlevel": 1,
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "className": "KvantumPlugin",
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "debug": false,
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]:     "version": 395520
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: }
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.factoryloader: Got keys from plugin meta data QList("kvantum", "kvantum-dark")
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: qt.core.plugin.factoryloader: checking directory path "/usr/libexec/styles" ...
Oct 30 09:10:05 charon org.freedesktop.impl.portal.desktop.lxqt[368070]: xdp-lxqt: Desktop portal registered successfully

Thanks, David

@lgKh The QT_DEBUG_PLUGINS output said:

root@charon:/home/amonra/Downloads# export QT_DEBUG_PLUGINS=1
root@charon:/home/amonra/Downloads# cd /opt/DeepSkyStacker/
root@charon:/opt/DeepSkyStacker# ./DeepSkyStacker
2026-10-30T09-10-04Z
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/platforms" ...
qt.core.plugin.factoryloader: looking at "libqxcb.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/platforms/libqxcb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "xcb"
        ]
    },
    "archlevel": 2,
    "className": "QXcbIntegrationPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("xcb")
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/platforms" ...
qt.core.library: "/opt/DeepSkyStacker/plugins/platforms/libqxcb.so" loaded library
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/platformthemes" ...
qt.core.plugin.factoryloader: looking at "libqgtk3.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/platformthemes/libqgtk3.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformThemeFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "gtk3"
        ]
    },
    "archlevel": 2,
    "className": "QGtk3ThemePlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("gtk3")
qt.core.plugin.factoryloader: looking at "libqxdgdesktopportal.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/platformthemes/libqxdgdesktopportal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformThemeFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "xdgdesktopportal",
            "flatpak",
            "snap"
        ]
    },
    "archlevel": 2,
    "className": "QXdgDesktopPortalThemePlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("xdgdesktopportal", "flatpak", "snap")
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/platformthemes" ...
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/platforminputcontexts" ...
qt.core.plugin.factoryloader: looking at "libibusplatforminputcontextplugin.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/platforminputcontexts/libibusplatforminputcontextplugin.so, metadata=
{
    "IID": "org.qt-project.Qt.QPlatformInputContextFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "ibus"
        ]
    },
    "archlevel": 2,
    "className": "QIbusPlatformInputContextPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("ibus")
qt.core.plugin.factoryloader: looking at "libqtvirtualkeyboardplugin.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/platforminputcontexts/libqtvirtualkeyboardplugin.so, metadata=
{
    "IID": "org.qt-project.Qt.QPlatformInputContextFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "qtvirtualkeyboard"
        ]
    },
    "archlevel": 2,
    "className": "QVirtualKeyboardPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("qtvirtualkeyboard")
qt.core.plugin.factoryloader: looking at "libcomposeplatforminputcontextplugin.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/platforminputcontexts/libcomposeplatforminputcontextplugin.so, metadata=
{
    "IID": "org.qt-project.Qt.QPlatformInputContextFactoryInterface.5.1",
    "MetaData": {
        "Keys": [
            "compose",
            "xim"
        ]
    },
    "archlevel": 2,
    "className": "QComposePlatformInputContextPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("compose", "xim")
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/platforminputcontexts" ...
qt.core.library: "/opt/DeepSkyStacker/plugins/platforminputcontexts/libcomposeplatforminputcontextplugin.so" loaded library
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/styles" ...
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/styles" ...
Loading translator file [ "qt_en_GB" ] from path:  "/opt/DeepSkyStacker/translations"
Loading translator file [ "DeepSkyStacker_en_GB" ] from path:  ":/i18n/"
Loading translator file [ "DeepSkyStackerKernel_en_GB" ] from path:  ":/i18n/"
Operating System name: Ubuntu 26.04.1 LTS
Build architecture: x86_64-little_endian-lp64
Current architecture: x86_64
CPU Type: Intel(R) Pentium(R) CPU G4560 @ 3.50GHz
Physical Cores: 1
Logical Cores: 16
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/iconengines" ...
qt.core.plugin.factoryloader: looking at "libqsvgicon.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/iconengines/libqsvgicon.so, metadata=
{
    "IID": "org.qt-project.Qt.QIconEngineFactoryInterface",
    "MetaData": {
        "Keys": [
            "svg",
            "svgz",
            "svg.gz"
        ]
    },
    "archlevel": 2,
    "className": "QSvgIconPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("svg", "svgz", "svg.gz")
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/iconengines" ...
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/imageformats" ...
qt.core.plugin.factoryloader: looking at "libqgif.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqgif.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "gif"
        ],
        "MimeTypes": [
            "image/gif"
        ]
    },
    "archlevel": 2,
    "className": "QGifPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("gif")
qt.core.plugin.factoryloader: looking at "libqtiff.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqtiff.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "tiff",
            "tif"
        ],
        "MimeTypes": [
            "image/tiff",
            "image/tiff"
        ]
    },
    "archlevel": 2,
    "className": "QTiffPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("tiff", "tif")
qt.core.plugin.factoryloader: looking at "libqicns.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqicns.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "icns"
        ],
        "MimeTypes": [
            "image/x-icns"
        ]
    },
    "archlevel": 2,
    "className": "QICNSPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("icns")
qt.core.plugin.factoryloader: looking at "libqico.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqico.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "ico",
            "cur"
        ],
        "MimeTypes": [
            "image/vnd.microsoft.icon",
            "image/vnd.microsoft.icon"
        ]
    },
    "archlevel": 2,
    "className": "QICOPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("ico", "cur")
qt.core.plugin.factoryloader: looking at "libqtga.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqtga.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "tga"
        ],
        "MimeTypes": [
            "image/x-tga"
        ]
    },
    "archlevel": 2,
    "className": "QTgaPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("tga")
qt.core.plugin.factoryloader: looking at "libqsvg.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqsvg.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "svg",
            "svgz"
        ],
        "MimeTypes": [
            "image/svg+xml",
            "image/svg+xml-compressed"
        ]
    },
    "archlevel": 2,
    "className": "QSvgPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("svg", "svgz")
qt.core.plugin.factoryloader: looking at "libqwbmp.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqwbmp.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "wbmp"
        ],
        "MimeTypes": [
            "image/vnd.wap.wbmp"
        ]
    },
    "archlevel": 2,
    "className": "QWbmpPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("wbmp")
qt.core.plugin.factoryloader: looking at "libqjpeg.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqjpeg.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "jpg",
            "jpeg",
            "jfif"
        ],
        "MimeTypes": [
            "image/jpeg",
            "image/jpeg",
            "image/jpeg"
        ]
    },
    "archlevel": 2,
    "className": "QJpegPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("jpg", "jpeg", "jfif")
qt.core.plugin.factoryloader: looking at "libqwebp.so"
qt.core.plugin.loader: Found metadata in lib /opt/DeepSkyStacker/plugins/imageformats/libqwebp.so, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "webp"
        ],
        "MimeTypes": [
            "image/webp"
        ]
    },
    "archlevel": 2,
    "className": "QWebpPlugin",
    "debug": false,
    "version": 395776
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("webp")
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/imageformats" ...
Color scheme is:  Light
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqgif.so" loaded library
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqtiff.so" cannot load: Cannot load library /opt/DeepSkyStacker/plugins/imageformats/libqtiff.so: libtiff.so.5: cannot open shared object file: No such file or directory
qt.core.plugin.loader: QLibraryPrivate::loadPlugin failed on "/opt/DeepSkyStacker/plugins/imageformats/libqtiff.so" : "Cannot load library /opt/DeepSkyStacker/plugins/imageformats/libqtiff.so: libtiff.so.5: cannot open shared object file: No such file or directory"
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqicns.so" loaded library
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqico.so" loaded library
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqtga.so" loaded library
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqsvg.so" loaded library
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqwbmp.so" loaded library
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqjpeg.so" loaded library
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqwebp.so" loaded library
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/accessible" ...
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/accessible" ...
qt.core.library: "/opt/DeepSkyStacker/plugins/iconengines/libqsvgicon.so" loaded library
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/plugins/accessiblebridge" ...
qt.core.plugin.factoryloader: checking directory path "/opt/DeepSkyStacker/accessiblebridge" ...
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqgif.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqicns.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqico.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqtga.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqsvg.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqwbmp.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqjpeg.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/imageformats/libqwebp.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/iconengines/libqsvgicon.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/platforminputcontexts/libcomposeplatforminputcontextplugin.so" unloaded library 
qt.core.library: "/opt/DeepSkyStacker/plugins/platforms/libqxcb.so" unloaded library 
root@charon:/opt/DeepSkyStacker# 

AFAICT it's not even looking for lxqt, so I suspect that @JKSH was correct in suspecting that there's no support for that in the QPA code. Guidance on how to phrase the request for lxqt support would be excellent.

What do I need to do to get my Qt application to use a dark theme on Lubuntu?

The style I have set by default is "Fusion". On Windows the application changes according to which Windows theme I'm using but I can't see how to get this to work on Lubuntu.

The OS theme is normally exposed to Qt via the application palette. See:

• https://doc.qt.io/qt-6/qguiapplication.html#palette
• https://doc.qt.io/qt-6/qevent.html#Type-enum (ApplicationPaletteChanged event)
• https://doc.qt.io/qt-6/qstylehints.html#colorScheme-prop
• https://doc.qt.io/qt-6/qt.html#ColorScheme-enum

I would first check if you get the expected values when you query the above, or if you receive the ApplicationPaletteChanged event when you change the OS settings.

If not, that suggests that OS theme integration is missing from the QPA layer, so you'd want to raise feature request at https://qt-project.atlassian.net/. I suspect this might be the case as Lubuntu does not use GTK.

Also, please do not post other people's email addresses publicly.

Could you please invite me to your Slack workspace?
Also I think you should invite me to Git repo for creating PR.

Best regards.