AFAIK, it depends on where this community originated in which this conversation happens.

• If it's a beehaw community: lemmy.world users can only talk to other lemmy.world users
• If it's a lemmy.world community: beehaw users can only talk to other beehaw users
• If it is hosted anywhere else: I give up, I cannot make sense of it.

Please notify me if someone knows the answer. I tried to understand it using this great explanation with examples.

I also wonder what would technically happen if beehaw users could not see comments from defederated instances in other instances. How would they see a back and forth? Would they see the same level of indentation? Would they see other users from federated instances replying to comments which do not exist?