Plasma has been updated to 6.6.1 this week, hopefully your display issues will be solved. If they aren't, there's likely either a crash or the NVIDIA drivers are misbehaving.
Getting logs will show you which one, or if something else is going on. Also check the Crashed Process Viewer. If you have crashes related to kwin, plasmashell or something else that's system related, that will probably be linked to this bug. If you have crashes, let us know and we can help figure out what's happening.