As I understand it, Proton is how my first game, Mooselutions, can be played on the Steam Deck without any extra work on my part. If you ship a game on Steam for Windows, it's just automatically available on the Steam Deck via Proton. You have to make some adjustments to your Windows build so it plays well and looks good, but otherwise it's totally viable. Mooselutions got Steam Deck approved without any need to do a straight Linux port. Gaben delivers.