Why YSK: Beehaw defederated from Lemmy.World and Sh.itjust.works effectively shadowbanning anyone from those instances. You will not be able to interact with their users or posts.
Edit: A lot of people are asking why Beehaw did this. I want to keep this post informational and not color it with my personal opinion. I am adding a link to the Beehaw announcement if you are interested in reading it, you can form your own views. https://beehaw.org/post/567170
But can C see A through B?
My understanding is that Lemmy isn’t peer-to-peer, it’s more like hub-and-spoke, relative to the instance that the community is on.
So if users on B and C are interacting with a post on A, then it’s the responsibility of A to be the postman and handle the syncing between A<>B and A<>C; B and C don’t directly talk in this case.
Thus, nobody outside of Lemmyworld sees posts from Lemmyworld, because Beehaw doesn’t accept them, and therefore doesn’t pass them along to the other instances, either.