I am currently playing Red Dead Redemption 2 on my deck, performs well enough (the major concern is the affect to the battery if playing handheld). Keyboard required for first time set-up (virtual keeb didn't work).

Others:

No Man's Sky - endless playability imo and was my go to when I purchased

Planet Zoo - I haven't actually played on deck yet, but I got my desktop setup where I only need to use the mouse, and plan to try the strategy on my deck.

Dofromantik - this is a relaxed puzzle game that is very good on deck

Podman - containerization is a game, and the deck is a Linux computer after all :)