To get past the first time setup screen, you need to launch the game in desktop mode. Choose "windowed" and then it will work in game mode. "Fullscreen" will only show a black box in game. In game mode windowed will fill the screen.

It's not unreadable but may be too small for some people.

Fullscreen was just a black box.

For the first time setup only, if you are in game mode no controls will work. You have to get past that screen in desktop mode first before it can be controlled in game mode.

It runs slower than it should. It's not a Steam Deck specific problem, but the slowness people reported many months ago is still there and affects the Steam Deck too.