When I go full screen on wayland apps, I see freezes. I cannot say exactly under what circumstances this problem appeared. However, I installed some side effects but removed them soon after. Also, when installing, I didn't have such a problem on kde plasma 5.23.1. Now I have the mesa driver 21.3.1 installed which has been updated too. The rendering quality is OpenGl 2.0, switching to 3.0 does not solve the problem.
However, for unknown reasons, the breakdown disappears when the "Show FPS" effect is turned on. Perhaps the solution to the problem is hidden in the principles of the "Show FPS" effect.
This problem is relevant not only for gwenview, but also for mpv and for the firefox floating window, all these apps run on wayland, not xwayland. There are no such problems on xwayland.
Also, I repeatedly created a new user, while the problem persisted, which indicates that there were no problems with user configs.
Also, there are no problems with the "maximize" effect. 
When running from the terminal, apps do not give errors except for gwenview (QWaylandShmBuffer: mmap failed) 



SOFTWARE:
Linux/KDE Plasma: 
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.88.0
Qt Version: 5.15.2