I'm not sure as I haven't seen it in action, but it sounds like Mastodon's official Groups feature might be somewhat Facebook-groups style?
It's on the roadmap as being under development. However, it is very overdue (it was supposed to be finished in 2022) so I've no idea if they've hit some kind of roadblock?
Actual working groups options on here include Guppe & Chirp & Friendica groups which are special accounts that repeat what is posted to them: