Since Qt 6.4.2 (or maybe 6.4.1) the rendering of fullscreen windows is broken on Android - the window is rendered behind the Android navigation bar which hides part of its content. If the window is created with:

setWindowFlags(Qt::Window);
setWindowState(Qt::WindowFullScreen);

you get the correct layout on Qt < 6.4.2 (tested on 6.3 and 6.2) and the broken layout with the current 6.4.2.