how does that download get me an activation key for it? As far as i know, you cannot just pay for one license of LTSC

I'm going to keep it real with you bro, I don't remember how it works, but the video below has been saved in my YouTube watch later for a few months and I think it's what I followed when I tried (I eventually moved onto Linux anyway):

https://youtu.be/s9dYV75sY3s?si=iIlg_0JDDMe8GWqI

and that video conveniently advertises an OEM key reseller as a sponsor.

G2A legit, Massgrave otherwise