From the ban/restrictions policy: “Steam Deck: Destiny 2 is not supported on Steam Deck unless Windows is installed and running. Players who attempt to launch Destiny 2 on the Steam Deck through SteamOS will be unable to enter the game and will be returned to their game library after a short time. Players who are not accessing Destiny 2 through Windows and attempt to bypass the SteamOS/Proton incompatibility will be met with a game ban.”