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.
Personally I find pirated games to be a bit of a pain to install on the Deck. I’d go with Windows for that use case.
It’s dead easy under Bazzite using Lutris or Bottles. Maybe I should write up a guide and post it here at some point.