Hide QMainWindow from task bar and task switcher

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Hello everyone,

for my Qt application I want to create multipleMainWindows (derived from QMainWindow), but they should not appear in the task bar or in the task switcher (alt + tab). I found this stack overflow thread, but none of the suggested solutions worked.

Using a hidden QMainWindow as parent:

QMainWindow hiddenParent;
MainWindow window(&hiddenParent);
window.show();

The Window is still shown in the task bar and the task switcher.

Setting any combination of the Qt::Dialog, Qt::Tool and Qt::CustomizeWindowHint flags:

MainWindow window(nullptr);
window.setWindowFlags(Qt::Dialog | Qt::Tool | Qt::CustomizeWindowHint);
window.show();

The window does not show up at all, although the application is running, or the window is still visible in the task bar and the task switcher.

Setting the Qt::SubWindow flag:

MainWindow window(nullptr);
window.setWindowFlags(Qt::SubWindow);
window.show();

The Window is still shown in the task bar and the task switcher.

Setting the Qt::ToolTip flag:

MainWindow window(nullptr);
window.setWindowFlags(Qt::ToolTip);
window.show();

The window does not show up in the task bar or the task switcher, but it also loses the window decorations.

Is using QMainWindows even the correct approach when I have multiple completely independent windows?
I am working with Qt 6.0.2 on Ubuntu 20.04, however I also want to run the application on Windows.

Thank you very much in advance!