https://doc.qt.io/qt-6/qml-qtmultimedia-windowcapture.html#window-prop
It is said that it should be a Window but it is actually not the case. It requires a QCapturableWindow which is not a QWindow.

I see 2 ways to address this:
1. Correct the doc so that it tells users that QCapturableWindow is needed
2. Wrap QWindow somehow into a QCapturableWindow

Personally speaking, I hope the latter can be adopted since otherwise users have to manually pick one from the list returned by capturableWindows (and probably also by looking into each description and validity).