I had the most fun with Vampire Survivors - addictive, relatively short bursts, but suitable for longer sessions. Dirt cheap.

I also liked MultiVersus… before it became a micro-transaction filled abomination. The core gameplay loop is still great tho.

General recommendation: Pick single player games from 3-4 years ago and back. The ones you were really interested in when they came out, but did not yet get around to playing them. Due to their age, they are almost guaranteed to run well on Deck, and they provide hours upon hours of fun. That’s my strategy at least :)