Itβs pretty easy to sum up. The admins on beehaw decided to break federation with a couple of other instances including lemmy.world. Their reasoning being that the open registration policies and relative lack of oversight in those instances were incompatible with the space they wanted to create on beehaw. What this means is that users from lemmy.world cannot interact with users on beehaw and vice versa.
The technical details of how all this works are a bit more complicated, but thatβs the basic gist.