you can make KWIN Hide kde effects if it detects the app is being rendered at true full screen since the user cant see the effects anyways that allows the gpu to focus more in the app and better performance that would also help low end hardware (like mine)
plasma already has System Settings → Display and Monitor → Compositor → Allow applications to block compositing. most games and fullscreen apps flip that and kwin drops effects while they are up.
for a stubborn app: Window Management → Window Rules → add the app → Appearance → Block compositing → Force yes.