Out of the box, the Steam Deck comes with SteamOS 3 Linux and overall apart from early quirks and bugs it does work very well but they're now providing Windows drivers — with a big caveat.
This was announced on Steam today, for those who do want to put up with Windows (not me). There's a few notes they included on it but the biggest and most important is that Valve will not actually be supporting Windows on Deck in any way. It was put very clearly as Valve said "we are providing these resources as is and are unfortunately unable to offer 'Windows on Deck' support".
People are free to do what they want with it, unlike more traditional "consoles" but the point is that for official support, you need to use SteamOS.
The quick notes Valve included:
- For now you can only perform a full Windows install. While Steam Deck is fully capable of dual-boot, the SteamOS installer that provides a dual-boot wizard isn't ready yet.
- Also for now, you can only install Windows 10. Windows 11 requires a new BIOS that is currently in the pipe (which provides fTPM support) and will be shipping soon.
- Drivers are provided for GPU, WiFi, and Bluetooth. Audio drivers are still in the works with AMD and other parties - but you'll still be able to use Bluetooth or USB-C audio with Windows on Deck.