Yakuza 0 is a great entry point to the series and runs really well on the Steam Deck. I recently finished Dredge and really enjoyed it on the Deck. Lonely Mountain Downhill is a enjoyable skill-based mountain biking game that's a lot of fun to explore and has a ton of content. Snowrunner is a chill game that works well on the Deck too...it's kinda like Dark Souls for trucks, but meditative. Hollow Knight is great and looks really good on the OLED screen. Pretty much any of the Fallout games are a good choice; New Vegas is probably the best overall but you'll need to use Desktop Mode to get some community patches in there while Fallout 4 is not as good story-wise but has better moment-to-moment gameplay feel. Hades is a great run-based roguelike that looks and works great on the Deck. I played the entirety of Jedi Fallen Order on the Steam Deck and it was great. Dead Cells and Scourgebringer are great action roguelikes that feel great to play and run well on the Deck. And while Baldurs Gate 3 is Larian's latest triumph, it can run into performance issues in the latter half of the game on the Deck; Divinity: Original Sin 2 was their prior game and it runs very well on the Deck and is a great game in its own right.

There's probably a lot more, but that's off the top of my head!