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.
I use repacks almost exclusively, and it’s one major reason I haven’t installed bazzite on my ally (that and game pass). It’s just stupid easy to hit install and not worry about compatibility.