nope.. the OS is completely modified as well, which was developed by the Xbox team.
although that version of Windows will probably in the future be made available to other Windows handhelds.
but for now it seems it's the only system to get it (probably easier to first work on 2 systems instead of every Windows handheld)
this version of Windows instantly boots into a game mode with a console like menu.
it completely deactivates most Windows processes, so not even the desktop environment is booted up unless you manually go into desktop mode (which is also how Steam OS works).
and apparently through these optimisations they massively improved battery life, and I assume also performance... as with no exporer.exe running, no start menu running (which is now an app in Win11), probably tons or related processes to these also not running, there should be way less bogging game performance down.
so this does seem to take a lot of inspiration from the Steam Deck