I mean, the Steam Deck can dual boot Steam OS and Windows 11. I have a 2TB USB C SSD that is a full Win11 install.

I expect I could use that same SSD on the Steam Machine.

Instructions:

Win 11 Install:

aomeitech.com/…/install-windows-11-on-external-ss…

Steam Deck Boot Menu:

Turn off your Steam Deck entirely.
Press and hold the Volume Down (-) button and press the Power button.
Release the buttons when you hear the chime. This will load the Boot Manager.
Select your External USB/SD Drive using the D-pad and press ‘A’.

SSD:

kingston.com/…/xs2000-external-usb-c-solid-state-…