Update 2: Well, I think I found the problem: The GeForce GPU applies some anti-aliasing, and it apparently causes trails of scrambled pixels when the pointer moves across certain backgrounds. I experimented (for hours!) with different combinations, and I finally eliminated the effect in Facebook within my Brave browser. (Interestingly, I never had the problem in any other browser.) IT DID NOT ELEIMINATE THE EFFECT IN OBSIDIAN. I managed to diminish the effect, but it still exists as an annoyance although it does not make the app useless anymore.
I’m beginning to see what the Obsidian user community is like: Not tech addicted; lots of MAC users versus real computer users (UNIX, Linux, even Windows…).
This web site is awesome, BTW. If Obsidian had been DESIGNED instead of being assembled as Frankenware, it might have eliminated, upstream, a lot of the problems I see on this forum today. It is totally feature-rich, but the features keep getting added piecemeal instead of being designed into architected solutions.
On the other hand, if the originators had tried to design a coherent system instead of opportunistically assembling and tweaking off-the-shelf components, there might be no Obsidian at all. I can see that having a working system to improve upon might be preferable to waiting for something to materialize in the future.