From what I know, most guides on piracy on steam deck involves running the game through Steam’s launcher as a “Non-Steam Game” which kinda feels sketchy to me, since the Steam Launcher portion of SteamOS is not open source, and they could be phoning home to Steam’s servers and reporting me as a pirate. Maybe they don’t go hard on pirates for now, but at any point in the future, they could pull a Nintendo move.
Ive used it for 1.5 years with absolutely no issue. I made a separate steam account just in case, but honestly even if i couldn’t use steam I’d still never put windows on there. Id much rather keep linux on it and just run games with lutris like people who have linux gaming pcs do. Steam makes it super easy and convenient but it isnt necessary for linux gaming.