To support decentralization and spread, should lemmy.world close registration at some point to prevent a performance overload due to too many users? Of course, if registration is disabled, there could be a hint placed somewhere near that from other instances you can interact with content on lemmy.world just like you had registered on it. There could be a link to join-lemmys instance overview.
Isn’t the intent of federation, however, that every instance should have access to every community? So even those small instances be able to access the same communities.
Not seeing something means you’ve intentionally defederarated them (or maybe they’ve defederarated you?)
Or a server is dying somewhere.