I had no issues with this game and I was able to play through everything no problem.
Worked great out of the box. When the game starts, you'll have to use a couple educated guesses to figure out what button gives the game input for the keyboard key they show on screen, but it's pretty natural and didn't take me more than a few seconds to figure out. Lovely little experience on the Steam Deck, it felt great to play Teacup on a handheld.
It didn't show controller layout only keyboard but was fine playing with the controller.
I played it in Desktop mode on an external monitor so I'm not sure how it would fare in handheld gaming mode, but considering that the game is also on Switch I can't imagine any issue regarding it while mobile. As for my experience I had no issues whatsoever.
