After a brief period of testing, Lemmy.ninja has transitioned to the use of a block list for instances. This means that all Lemmy instances (and their communities) are accessible at Lemmy.ninja. Admins reserve the right to ban a Lemmy instance in the future, but as of right now there are no instances on the block list. This should give you unfettered access to all Lemmy content regardless of server.

That said, Lemmy.ninja still has site rules, which you can see on the sidebar after you log in. If a Lemmy instance is discovered to violate those rules, admins reserve the right to block that instance at their sole discretion.