I remember when Kagi.com was a payment platform, one of the earliest ones and the first one I used back in the day. Great guys, too bad they've been shafted hard by a dishonest customer. Feels a bit weird to see the name used by a search engine now.
>Don't you need a MS developer key to build it or something now?
I built it myself a couple of months ago and I didn't need any key. I just cloned the source from GitHub and compiled it following the build instructions.
Well, MultiMC is open source so you can always disable the account check. I'm sure there's a patched fork already somewhere, however I'm not sure whether this is legal or not.
>Microsoft mines phone numbers
This seems to be more or less standard practice now. Happened to me with several companies. They let you sign up with just an email address, then after a few days or weeks they block your account because of "suspicious activity" and ask for a phone number. Very annoying.
Try Mineclone 2. It's an open-source libre Minecraft clone which runs on top of the Minetest voxel engine and has 99% (almost) feature parity with MC 1.12, can be expanded with hundreds of mods and it runs natively in Linux. You'll be surprised at how polished it is already. In fact, it's so similar to the original Minecraft 1.12 in both gameplay and appearance that it surprises me that Microsoft/Mojang hasn't threatened a lawsuit (yet). I downloaded it just out of curiosity some time ago and now I play it more often than Minecraft itself because of all the fun mods I can try.