You can start, and even somewhat play the game with Steam's Keyboard (WASD) and Mouse layout on the Steam Deck, but MareQuest definitely requires a controller layout to have full functionality. Luckily making a layout is really simple. I uploaded mine to the community if you'd like to try it. Everything else works just as well as desktop, right from the get go! Resubmitting to fix a typo in my summary title, not that it matters much.