Fumanstu YAY! more game time for stu! Exciting!
You’ve probably got a ton of things that work well in your library matey, but I will say Elden Ring is remarkable on the machine. I’ve enjoyed Darktide but that’s with the caveat that that is despite its many buggy issues. NMS works well. Deep Rock Galactic is a joy (and quite cheap and also I’m available for coop in the steam deck any time).
I’ll have a think more specifically and a look at my most played games and post back with more.
I would give it some vanilla time before you do anything like add plug-in extensions etc. Valve have done an amazing job of fixing things many of the plugins were built to fix in the first place.