I’m sure it’s sufficient for two players, but I don’t know how the game rearranges the interface with four. It might be a little crowded.

I can confirm that Barony is a fun couch coop experience for two on a steam deck, so long as you are prepared to die and have to start over a lot. It might be tricky with four players, as there is a lot of inventory menuing. You might need a really large screen.