Incorrect painting of widget on the first show

After upgrading to qt version 6.2.3 from qt5 I faced the problem with starting the app in the maximized mode. The widget is first painted with it's normal size and then repainted fine. The intermediate state is shown on the gif below.

The code of the app from the giff comes together with Qt (my version is Qt-6.2.3) and called "styles" (path is Qt/Examples/Qt-6.2.3/widgets/widgets/styles) or can be found on the qt.io. I have just changed `widget.show()` to `widget.showMaximized()` in main.cpp.

I figured out that sometimes widget starts fine, but this is rather rare. Also the more complicated widget is, the more time it takes to correctly paint it on the first show.
In the example from the gif the start is so quick that it is almost invisible, but in the heavy app I'm working with this slow startup really catches the eye.