KDE dots & stripes glitch when waking from sleep

Very patriotic.

I had something that might or might not be similar:

Also artifacts looking like yours, and also with Wayland; but:

Only on Firefox and I'm not sure if after sleep or in my case was after using fullscreen only.

They went away after the last mesa update, is yours the last version too?

Just to check and be sure its not hardware, have you done a clean boot and run a stress test?

Run memtest. Stuff like this happened a lot when I had bad RAM. Might not be your case but still a good thing to rule out.