Title, basically.

Unless admins of specific instances are publishing defederation lists, it seems like it's impossible to tell without visiting a community on a defederated instance from your home instance only to see "no posts." While I like federation overall, I feel like most users are going to end up with a few accounts or setting up their own Lemmy instances just so that they can see stuff from all other instances without running into errors.

Maybe adding some sort of message when viewing a community from an instance not federated with it would be a good idea, with a generic catch all of "Your home instance is not federated with the instance that this community is on. Please contact your instance administrator for details" with the option for instance admins to customize the message per instance if they want to. I'm not really a programmer-type so I wouldn't know if that was even feasible.