Fediverse

Is there a way to bring them all together? Even within one service, like Mastodon or Lemmy, my experience is that you eventually hit the wall of "oh that topic is on another instance" and you can't simply get all the topics you want to follow in one feed. Federated means "held together," or "unified," right? But I must be using it wrong or missing something huge because the end experience seems mainly characterized by fragmentation.