Valve has previously announced that the Steam Deck will ship with their custom Steam OS 3.0 based on Arch Linux but that the user would be able to install alternative operating systems such as Windows 10. When Microsoft recently announced Windows 11 they also increased the system requirements with the most contentious decision being the requirement of a Trusted Compatibility Module (TPM). The Zen 2 Van Gogh APU found in the Steam Deck features a firmware-integrated TPM which needs to be supported within the device BIOS to enabled compatibility with Windows 11. Valve has confirmed that they are working with AMD to support the requirement and are hopeful that they will be able to achieve this.

Greg Coomer - Valve Steam Deck designer There's work looking at TPM just now. We've focused so much on Windows 10, so far, that we haven't really gotten that far into it. Our expectation is that we can meet that.