We've seen a few reports of issues with Steam Deck so we're looking into them.
The first thing I noticed is the game was actually running at the wrong resolution by default. For some reason setting the resolution in options didn't do anything either. The latter was probably due to some kind of weird Steam Deck specific Proton issue.
To fix this, I updated to the latest Steam SDK so the game can detect whether it's running on desktop or Steam Deck. Now the game is forced into Steam Deck's native resolution (you'll see the resolution as AUTO in the settings) when running on device. You MIGHT have to delete and re-install the game to get this fix to really take.
You'll know you are in the right resolution if you don't see black bars on the top and bottom--also it was making the remapping panel and a lot of in game text look weird. This should all be resolved, and now you have a nice extra chunk of vertical space in the proper 16:10 aspect ratio.
I'm not actually sure how this fix will work when the dock comes out--but we'll cross that bridge when we come to it.