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 ☺️