With the last update "0.9.7a" many changes have been made to accommodate Steam Deck & Steam Machine. Currently, Valve needs to verify the game for Steam Deck for full support.
Changes made for Deck compatibility:
-All content is accessible using controller-only
-Full SteamInput API integration
-Steam Deck physical controller support / Steam Controller support
-No in-game settings need to be configured to use Steam controls, it's plug and play
-Controls used in text are automatically determined and displayed accordingly
-Text modified to look clear and at the minimum ppu on Steam Deck's native resolution
-Defaults to Steam Deck and Steam Machine native resolution on launch
More info on Steam Deck and Steam Machine compatibility will be published here or routed to a new post upon Valve's approval.