UnknownUnknown
WINEDLLOVERRIDES="winmm=n,b" %command%
Followed the instructions here: https://steamlists.com/maui-mallard-in-cold-shadow-how-to-set-up-steam-deck-via-proton/ The only change I did was that at the virtual desktop resolution I input the native Steam Deck resolution of 1280 by 800 and the game runs full screen.
The music was missing when played without the launch options. Sound effects were there from the start. Adding the launch options enabled music but disabled the video output. Then the protontricks part enabled the video and the game is fully playable.
Had to map the controller by hand according to the original manual and it worked. I later found out that another user had created a community layout that works great.
The game needs to be tweaked further after setting the custom launch options or else you won't get any window when you launch the game.
WINEDLLOVERRIDES="winmm=n,b" %command%
Install the game on the drive you installed Steam on and then install Protontricks. Enter "protontricks 987410 winecfg" without quotations in your terminal and then go to the Graphics tab and click "Emulate a virtual desktop". Then set the desktop size to your native resolution. I had to use AntiMicroX in order to use my gamepad.
Audio wouldn't work without setting custom launch options.
Fullscreen couldn't be enabled without further tweaks.
My controls that I remapped through Steam weren't detected. I had to use AntiMicroX to use a gamepad.
Correction to previous report; I managed to make the game run in fullscreen with music - works great. Xbox One S controller sort-of works (game is designed for Sega Genesis - 6 buttons controller, it does not support other controllers very well). Steam Controller does not work (but it doesn't on Windows either). Tweaks: https://github.com/ValveSoftware/Proton/issues/2712
Game itself works fine and performs well, BUT: fullscreen does not work (seems like it does not work on Windows either), music does now work (works on Windows), controller support does not work (mixed reports on Windows - based on Steam Reviews).
