I had issues with screen updates after the last major update. Some parts of the screen will not be updated and stay white or contain artifacts from another tab or window.
Using the control-key that highlight the cursor position will update the window.
I believe you might have the same situation like I had, with the driver installed but not providing hardware acceleration - [SOLVED] GT520 + linux54 5.4.85-1 + linux54-nvidia-390xx 390.138-2 = absolutely terrible performance. It may or may not be the cause of your screen artifacts, but maybe it is worth checking. And maybe the next step would be to check if the compositing is on (KDE turns it off on boot if it detects a problem with hardware acceleration, maybe it’s something similar for GNOME, I don’t know).
(You asked for ideas :))
Thank you very much. This exactly solved my problem.
However, I have to find out how to let the configuration survive the next update - since mhwd.conf is autogenerated.
Update: Created a file in /etc/X11/xorg.conf.d/ with the FILES-section only. This will be inserted into the final configuration.
Yes, this was my first idea, and it worked perfectly; then I moved the lines into nvidia.conf to keep it simple - from what I understand, it should survive updates. If not, I’ll go with a separate file, as you did.