We kept one going for five years in the local region. Had about 50-ish people to certain events at its peak, probably a few hundred active members (including inactive it was over 1300). But paying $180/year didn't feel worth it as soon as the pandemic hit. I was the main one paying it also.

Kind of shitty too because you can't really kill a Meetup group as long as someone is willing to pay for it. I stepped down as admin and some speed dating thing swooped in and started paying for it, so now the page is still up but there's only speed dating events on it now.

I think Meetup has almost doubled in price in the past 5 years, and it's gotten some major competition from Facebook's groups and events, so I wouldn't be surprised if it's on the decline. I don't think I'd bother to create a Meetup group nowadays, just create a Facebook group.

I do still use it to find some online events to attend periodically, though. Still haven't done any events with random people in person yet, just friends I know are vaccinated.

Most of the meetups I'm in have been going on for several years, at least.

My backpacking group is on meetup. I joined in 2016. Not sure when it was started, but it was a few years before that. Admittedly, the group existed in some form before Meetup did, but it has grown to over 2000 members on Meetup. There's a core group of about 50 or so who are very regularly active.

There's also a local hiking group, a python user group, a biking club, and a climbing club. Quite a few of these existed before meetup and will probably exist after meetup.

I think it depends on the group. I’ve been in several that have lasted multiple years. They tend to be focused on one specific hobby or demographic niche and then offer a wide variety of activities within that niche. Additionally, have multiple organizers and a large enough funnel of new joiners that it always feels big and welcome and established. I have no idea how they got to the stable position they’re in now, but these meetups are more like self-directed communities than they are going-somewhere-for-one-thing interest groups.