Lemmy.online was taken down, from what I can tell. Pretty much everyone told that admin what he was doing was a bad idea and something that no-one wanted. Most instances defederated the site and I think he gave up.

I think a key point that a lot of people don’t understand is that data from communities on different instances doesn’t replicate to your instance unless a user cross-subscribes to that specific community. If you build an instance and want !memes@lemmy.world to show up on your instances ALL feed, you have to subscribe to it with at least one account by browsing to your@instance.com/c/memes@lemmy.world and hitting the sub button. Only then will the content replicate.

Server federation between two instances doesn’t magically connect all the communities, but once the users have subbed, they’ll be able to see the content they want to see on these smaller instances. The process to get all the data replicated over is just a little more convoluted than it should be.