already did like at 2 AM... a friend of mine also tried to do it but it turns out that “Download or transfer over USB” only works if you own a kindle, which he doesn't... so there's that too
Definitely do not tell that friend to head to https://en.m.wikipedia.org/wiki/Z-Library and use one of the URLs listed there to go to that website and find and download a DRM-free backup copy of all the books they have bought and paid for in the past.