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.
It really, really isn’t. Adding a “non-steam game” is trivial via applications like Lutris, Heroic & Bottles. That’s quite literally how I play half my games, which are pirated.
As for why you would want to in the first place, gamemode is literally the only controller-friendly launcher that exists on Linux. No one’s bothered competing. As soon as one does pop up I’d imagine Bazzite will integrate it but until such time well ¯\_(ツ)_/¯