Hey there,
GIANT ROBOT GAME works well on Linux, so it'll show up as compatible with the Steam Deck (a Linux machine) but I want to make it clear that the game currently assumes keyboard & mouse.
So, while you can technically play the game on a Steam Deck, in practice, you will want to use a laptop or a workstation.
This may change in the future. I've often thought it might be fun to play the game using a controller. But I can't promise anything, since that'll need careful experimentation and probably major differences between mouse+keyboard gameplay and controller gameplay.
That being said, if you wishlisted this game hoping for playing it on a Steam Deck, please tell me!