At least you are off the tankie Lemmy instances. One more point for using MBin, which is better. There are other Lemmy instances that aren't managed by them, e.g. lemmy.world; still that doesn't prevent you from moving to MBin.
Point proven before i could add: The chats should be encrypted (there's an FEP somewhere)
Edit: now they made my point look wrong (it's actually right), heres the sup server source code on how they implement it themselves: https://github.com/thesupapp/server
Interaction between accounts from different servers.
For example, you signed in to a minetest server on mt.example1.com, then you want to play from another server in mt.example2.com, you "tell" your account instance to play on the remote instance and afterwards you are playing in the world from another server from your account instance
From the remote instance's perspective your character is in the world as "YourUsernameHere@mt.example1.com"