Think of it as people using different email clients. When you’re using Gmail, that doesn’t stop you from emailing people on Yahoo or Hotmail right? It’s the same with lemmy. Here people signup on different servers and you can talk to them. Think of it like a twitter user liking an Instagram post without leaving twitter. They can follow any Instagram user and see their posts if they follow them but they don’t have to log into Instagram. And that’s what Meta is trying to do with threads.