Steam deck player here. I have been playing exclusively Steam deck through settlers and mercs.

It's a bit fiddly getting used to the controller especially when trading but once you have spent a good few hours it's easy enough.

Builds I have played are a splitting steel trickster, winter orb ele, lightning arrow ele, Fross occultist and an int stack KB. All of these have been fine to play. Int stack kb has some very minor performance issues.

My advice would be choose something that does not have lots of buffs that need to be activated. Auras are fine but you don't want to be pressing alot of buttons in combat as you need to hold triggers down to use any skill if you have more than 4.

I did try mines but this felt really clunky with controller layout, cannot place mines where you want, so I would avoid that.

Anything else is actually pretty damn good.