I'd recommend following the steps at https://invent.kde.org/plasma/powerdevil/-/blob/master/READM... to disable brightness control. You can switch to X11 too, but for some reason I get screen tearing and blocky incomplete updates I haven't looked for a workaround yet.

  systemctl --user edit plasma-powerdevil.service
  [Service]
  Environment="POWERDEVIL_NO_DDCUTIL=1"

EDIT: I tried switching to Wayland on Arc and am getting stuttery mouse cursor movement at around 36 FPS. I wonder what's wrong...