I'm involved in my local FIRE community. Honestly, if you just make a Facebook or Meetup group, and post a link in the MMM forums and on Reddit, you'll have a lot of people show up (assuming you're in a city and not Bumfuck, Nowhere). Our group mostly involves online discussions, and we do meetups here and there depending what the rules are - the Covid rules have been changing a lot in my area over the last couple years, so sometimes we can do indoor things, sometimes outdoor, and sometimes nothing. We're pretty low-key and usually meetups are just a group of us hanging out for a few hours at a park, the library, or someone's back yard. Sometimes a walk or easy hike or something like that.