Hey there, Destiny 2 only runs on Windows; the Steam deck uses a Linux-based OS called SteamOS and a compatibility layer called Proton which the game will not run on. However if you install a genuine copy of Windows on a Steam Deck, it should run Destiny 2 just fine. I am not sure what 'non-custom' hardware means in terms of PCs, as they're all made from different specifications of hardware, different components made by different companies, the Deck and Machine are just two more PC variants. But it's all down to the OS really. The Steam Machine will be the same, it will run on SteamOS as standard, and will require a Windows installation before it can play Destiny 2.