Minecrosoftcraft
So, turns out I found a way to happily play my legal minecraft. The trick, of course, is to avoid as much microsoft garbage as possible.
It seems that despite confirmation emails and successful logins, my Mojang account wasn't considered migrated.
So I went through all of the steps again, but this time in Firefox on my Void Linux machine. No Microsoft "security" (ha!) or invasive and offensively bad mechanisms involved.
A browser that follows standards, and emails to confirm.
And it worked.
Conveniently, Prism Launcher stores microsoft account credentials so there's only the need to prove yourself 15 times (good work, microsoft) 1 time. Then the launcher will do it for you.
It's just too bad it was all built on Java, because hosting a server and playing uses about 14Gb of my 16Gb of memory.
I've only gone OOM a couple of times. eyeroll