This misconception with DRM making it unplayable on steam deck I think stems from 3rd party anti-cheat software flagging Linux players. Denuvo “works” fine on steam deck and Linux as a whole, same goes for anti-cheats. Developers always have the option to tune the anti-cheats to allow Linux players, but only some of them do.
Only dummies buy games before they’re available to the public. I thought this has been known since Watch Dogs (another Ubisoft game lmao).