I have perhaps solved it.
Last month this bug started to appear, after almost two years. It can be temporarily restored by “water waves” graphic settings (high → low), but this does not solve it (as Coleo91 mentioned). I tried to change other graphic settings, but no effect. I didn’t presume that it’s a hardware problem. But then i remembered that I have undervolted and underclocked GPU (to reduce heat emited to the room - because of this sweaty summer). I changed it back to my usual undervolted profile with standard 2250 MHz and this weird glitch disappeared. Voltage was apparently too low.
So try to disable GPU OC/UV tuning profiles.
My HW: Ryzen 5800X, Radeon 6800 XT.
