I probably need to install Windows, in order to run a proprietary glorified rsyncd that updates and SD card.

There was a thread about cheap licenses recently, where Moonman used some kind of weird channel to obtain one, and someone replied: "the ones sold at eBay for $25 worked for me".

Does anyone remember what it was about?

I didn't touch Windows for 20 years, since before XP and before "online activation".