I would pop that drive into another machine, install the OS from that machine - then put the drive back in and go from there. But yeah - it's a pain to work with stuff like that..
I wanted to install win11 on my own (unsupported) machine, refused to install and keep existing files etc, so it rolled back win 10. So I left it at that for now. (I only use windows for 1 game that I play - that does not work on linux at all).
Either way - nice of you to help him out!