Turns out the culprit is… Wayland!
I’ve resisted moving to wayland for years because I keep seeing people reporting issues, especially around gaming.
I switched back to X11 from the default Wayland session that KDE Plasma now offers and all of my issues are gone, including:
- regaining the approximately 10-15% performance loss I was experiencing on games
- getting rid of the damn sticky edge between my two monitors
- randomly having a game “lose” the mouse when I pan too quickly right - on wayland, this would kind-of “eject” the mouse, and I could click on the right desktop - not useful whilst trying to kill hordes of bugs! I thought this was some KDE silliness, but reverting to X11 - problem solved.
Wayland is supposed to be the simpler, faster, smarter display manager - but it’s still not ready for prime-time if it’s doing nonsense like this, and I personally think it was a mistake making it the default session.