[beeflet]

I owned a mojang account and didn't migrate it to microsoft. Now I just pirate the game whenever I want to play, it's pretty easy pollymc or pojavlauncher.

You can also play in multiplayer by going to server.properties of your server and setting online-mode=false

[johnisgood]

Yes, you can only join a server with that setting set to false.

The launchers for Linux are readily available, too.