The Steam Deck is available for worldwide shipping and several consumers have already received their units. A number of titles like God of War (2018), Deathloop, Sekiro: Shadows Die Twice and so on are playable on the handheld after being optimized for the same. However, there are still few unsupported games like Epic Games’ Fortnite.
Add Bungie’s Destiny 2 to the list. In its Steam Guide article, it noted that the title is “not supported for play on the Steam Deck or on any system utilizing Steam Play’s Proton unless Windows is installed and running. Players who attempt to launch Destiny 2 on the Steam Deck through SteamOS or Proton will be unable to enter the game and will be returned to their game library after a short time.” Furthermore, anyone who attempts to bypass this will receive a game ban.
The issue may have to do with anti-cheat measures. After all, Fortnite has been excluded due to Easy Anti-Cheat not being supported on the Steam Deck (despite Valve previously noting that it was working with Epic Games on support for the same). Destiny 2 uses BattlEye, which is supported, but it could be that Bunge doesn’t want to optimize for the same.
Plans could change but for now, don’t expect to enjoy Bungie’s looter shooter franchise on the go. At least, not through Valve’s handheld platform.