Selection rectangle not shown or partially shown

[Perdrix]

I have a "SelectRect" widget that is a child of an image display widget. It has the same dimensions as the image display and does:

setAttribute(Qt::WA_TransparentForMouseEvents);
setAttribute(Qt::WA_NoSystemBackground);
setAttribute(Qt::WA_WState_ExplicitShowHide);

I recently had a problem when in 3840x2160 resolution on my laptop where none of the stuff drawn by SelectRect::paintEvent() was shown on the display.

On my system I found that installing an earlier level of the video driver for the nVidia Quadro RTX5000 solved the problem.

However I just had a report of this stuff being only partially visible on another user's system

He's using Intel Iris XE embedded video.

Is there any chance that this could be partially a Qt (6.4) issue (I don't think so but ...)?

Thanks
David