Groups is what is missing from Mastodon. Real Groups that is. Where posts inside a group stay inside a group. You join or leave the group if you are not interested in that topic. Same as Matrix Rooms or Telgram groups. Currently Mastodon is just a stream of announcements and no real social connection. Individual threads are OK. But you'll never find that thread again after a few days.
Groups mean people can post in detail on that topic without woryying it'll bore their followers. People have multiple different topics that need not overlap.
Groups make a social connection. You'll get to know people.