I used to play factorio with my friend in local coop with Universal Split Screen with 2 mice and 2 keyboards. It ran perfectly, but the double mouse/kb setup were not easy, and iirc there were some bugs with zoom or something. Maybe this will help with that, I will try it again.
Factorio was the game where I forced myself to play with the Steam Controller. After that I loved to play with.
But to be honest, I still have issues with playing those games on a Steam Deck, because the Touchpads aren't reachable very well for me.
Hearing that it will get Controller Support is a very nice thing. Because now I can play the game on my Steam Deck again :D