Run game with mangohud
From Pengwings
MangoHud is the performance monitoring overlay used on the Steam Deck but it also works on desktop Linux.
To run game with mangohud simply set MANGOHUD=1 environment variable
In steam you can set launch command of game to this:
MANGOHUD=1 %command%
If you're using gamescope it has mangohud built in; you have to pass this argument to gamescope instead of using the env var:
--mangoapp
