“mouse flickers like crazy” … as in, mouse cursor shows & disappears rapidly?
if by chance you mean that the mouse motion isn’t smooth, it could be a wayland/xwayland issue. I’ve came accross few older games where the mouse movement stutters noticeably, but if I use PROTON_USE_WAYLAND=0 so the game will run with xwayland, it’s smooth as butter.






put it as environment variable in game’s settings in heroic. https://github.com/Heroic-Games-Launcher/HeroicGamesLauncher/wiki/Environment-Variables
this of course only works if you’re using proton AND wayland (EDIT: regular valve’s proton doesn’t have this, btw. only some souped up forks, like proton-ge)