I've got a confession to make. Since I left Google+ and Reddit two years ago I always missed the community approach of both social networks. Don't get me wrong I love XMPP (or Movim in my case) and Mastodon. I love their ease of use and the possibilities to communicate. I love the ease to set up a chatroom or a microblog in Movim. And I love that they are federated and operate without a giant company behind it that preys on my data. However both on Movim and Mastodon it's hard for me to have a structured conversation around one single topic (e.g. cycling or 3dprinting). It's for that reason that lately I've spend time on Lemmy. Lemmy is easiest described as a federated Reddit alternative. Communities are fundamental for Lemmy. Every post has to be posted in one of the communities. If the community doesn't exist the user can create one themself. Post don't get buried by hundreds of other posts and discussion threads are easy to follow. I'm currently on lemmy.ml which appears to be the most general purpose and the largest server in terms of subscribers but you can run your own server if you want to. The numbers of users of Lemmy is currently growing rapidly but only time will tell what portion of users remain active.
The beauty is that Movim, Mastodon and Lemmy (and all other federated social networks) serve different purposes so I don't have to choose. They can co-exist and enable people to optimize their online social needs.