Set up a mangohud config file, either

Set up a mangohud config file, either manually or with Mangojuice (found on bazaar). Then in Steam, add

mangohud %command%

mangohud %command%

to your launch options for the game you want the overlay on

Alternatively, you can just try the Steam overlay. It's a lot more useful nowadays

Set up a mangohud config file, either - Bazzite