@kazarts There is one other thing I can think of, you can create an isolated home environment for the appimage to run in, as follows.
In a convenient location in your home folder, create a folder called Iso-Krita (or whatever you think is a suitable name). In that folder, place the krita appimage file.
For simplicity, rename the appimage file to krita-5.1.5 because it’s easier to type than the standard downloaded file name.
Then create a folder called krita-5.1.5.home.
Then run the appimage.
The appimage will see the [own-name].home folder and use it for all its config and resources storage and so will create a totally fresh set of configurations and resources.
Those will be isolated from other system influences.
The screenshot above shows my 5.1.5 isolated environment. You can have different isolated environments for different versions and run them at the same time if you like.
The three subfolders .cache, .config and .local were created by the 5.1.5 appimage when it first ran and they contain what you’d expect them to contain.
Please try that to see if it fixes the problems.
@kayleeJ I’d suggest that you try the same thing to avoid system effects on krita.