Since everyone will likely give you varied answers I’m going to recommend this list from Protondb.

You can also see what Valve recommends here for another good batch of games.

Me personally, I’ve had great luck with Indie games, Story heavy single player games like Dispatch and for multiplayer, I can guarantee that Helldivers 2 works.

This is not a thing because of Deck.

Were you launching a game that requires online presences? Kinda seems like it.