After too much time spent on google I finally found this lightweight GUI + CLI tool that finds locally installed games (yes including non-steam games running under proton) and thought I’d spread the gospel!
Combeined with something like dropbox/onedrive/nextcloud, or rsync/borg/syncthing etc you’ve got yourself cloud backups too.
Zero configuration involved so far on my Steam Deck which is nice as well.
Forgive me if it’s old news ☺️
Its reliance on PCGW is problematic. Anyone can edit it and there are cases of the wiki paths being wildly incorrect. Good luck finding the config of the Game Pass version of Starfield at this location.