Windows now works on all Steam hardware, but Valve would prefer you didn't actually use it

Valve has released Windows drivers for all Steam hardware, including the Steam Deck and Steam Machine, enabling users to install Windows on these devices. However, Valve explicitly states it will not provide support for Windows on Steam hardware and users are on their own if issues arise. Currently, dual-booting SteamOS and Windows is not supported — switching OSes requires wiping the entire drive. Valve has indicated dual-boot support is planned for SteamOS's full launch.