Unknown module(s) in QT (Debian 11, Module packages already installed)

[Aario]

I cannot compile any Qt5 example that uses a plugin. This is the error I get:
Project ERROR: Unknown module(s) in QT: multimedia multimediawidgets
All I could find on internet was regarding installing necessary packages. But I have already done that.

For example, I cloned:
git://code.qt.io/qt/qtmultimedia.git
I switched to branch:
5.15.2
I rename the folder:
example
to:
example1
(see https://bugreports.qt.io/browse/QTBUG-65057?focusedCommentId=454875&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-454875 )
I have qt installed from debian 11 repositories:

$ apt search qt | grep installed | grep base
qtbase5-dev/stable,now 5.15.2+dfsg-9 amd64 [installed,automatic]
qtbase5-dev-tools/stable,now 5.15.2+dfsg-9 amd64 [installed,automatic]
qtbase5-doc/stable,now 5.15.2+dfsg-9 all [installed,automatic]

I can compile qt applications without plugin. So it is not a generic problem with compiling programs.
I have necessary plugin packages installed:

libqt5multimedia5/stable,now 5.15.2-3 amd64 [installed]
libqt5multimedia5-plugins/stable,now 5.15.2-3 amd64 [installed,automatic]
libqt5multimediagsttools5/stable,now 5.15.2-3 amd64 [installed,automatic]
libqt5multimediaquick5/stable,now 5.15.2-3 amd64 [installed,automatic]
libqt5multimediawidgets5/stable,now 5.15.2-3 amd64 [installed]

This is my debian version:

PRETTY_NAME="Debian GNU/Linux 11 (bullseye)"
NAME="Debian GNU/Linux"
VERSION_ID="11"
VERSION="11 (bullseye)"
VERSION_CODENAME=bullseye
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

Any idea how to fix above error is highly appreciated. Thanks in advance.

[jsulm]

@Aario said in Unknown module(s) in QT (Debian 11, Module packages already installed):

libqt5multimedia5/stable,now 5.15.2-3 amd64 [installed]
libqt5multimedia5-plugins/stable,now 5.15.2-3 amd64 [installed,automatic]
libqt5multimediagsttools5/stable,now 5.15.2-3 amd64 [installed,automatic]
libqt5multimediaquick5/stable,now 5.15.2-3 amd64 [installed,automatic]
libqt5multimediawidgets5/stable,now 5.15.2-3 amd64 [installed]

You did not install the dev packages

[Aario]

Yep. That solved the problem:

$ sudo apt install qtmultimedia5-dev