Are threads like this one about clubs/meetups on topic for the site? It's so far off from my concept of a "retrocomputing" SE site that I've got no idea what to think about it, but it's clearly not totally unrelated.
I'd say it's off-topic.
On the one hand, such meetups are of interest to retro enthusiasts (so as you say, it's not totally unrelated).
On the other hand though, answers to this question would have a limited geographical scope, and probably a short half-life — some meetups are long-lasting, but many aren't, and the information on them tends to move around so even external links might not be useful very long. An answer which is valid now might well be useless or misleading in a couple of years' time... Both these factors mean this seems like a poor fit for a StackExchange site.
This kind of question doesn't seem to fit SE very well. Its not off-topic exactly, but its a bad question. Thinking about what kinds of answers we would get to questions like this and I think they would be short, every answer would be equally valid, and would be mostly useless without links. None of that sounds like a good QA idea.
Questions about meeting have cropped up on other site metas in the past. Certainly on Genealogy and more recently on Motor Vehicles.
The consensus seems to be that suggestions of a meeting should be made in the chat room.
That would seem to be appropriate for this site too.
I'd argue it's conditionally off-topic.
I suppose if you can find a way to have a specific question of general interest and use on the topic of clubs/meetups, that could be quite topical. For example, a question about the history of the Home-Brew Computer Club where both Microsoft BASIC and the Apple 1 were famously introduced, that's should be topical.
A question such as "Are there any 8 bit Commodore clubs/user groups/meetups in the Portland, Oregon metro area?" would not be. I could answer such a question in the affirmative--but I see two reasons why that is a poor question. First, the question and its answer are not useful to people in Tampa (or anywhere else). Secondly, it's a request for information that may change in the future. Currently there is a Portland CUG, whose current meetings are held at this location on these dates, at these times. Any of that information may change in the future, causing a well-accepted answer to become completely wrong.
We have questions of selective interest now, but there are a lot of people who share those selective interests. I don't have an Amstrad CPC and am therefore not hugely interested in questions and answers about it. But even if the Amstrad users are a small segment of our userbase, it is not exclusive the way questions of gatherings based on geography are.