Fediverse

I've seen a lot of websites (not so much in the Fediverse, but small forums and spin-off forums) and the kinds of basis they have does affect whether people want to post there, and how the place grows. (I'll just call them instances, because they technically are but I'm not just talking about Fediverse instances, so the dynamics of cross-visibility between sites aren't really being considered)

Topic-based instances and goal-oriented instances seems like the best bet for a high-quality discussion community. I mean broad topics as well, consider mander.xyz or the former gtio.io, not just more specific ones like slrpnk.net. It can be limiting, but so long as you're secure enough with your ego that you don't need to chase high numbers to know you're stable and active, then I'd recommend it. The tough part is that you may not get as much casual exposure to start off with, by being on the same site as larger communities, you might need to be active (without being annoying) in crossposting good topics to make people aware your community exists.

National-based instances are also popular, probably because of shared language, cultural elements and local issues. But they are otherwise pretty compatible to general instances. They do have a place, I've enjoyed a couple on occasion, they have a place, but I do prefer the topic-based communities. There's no point limiting every topic arbitrarily by nation or state.

General instances (either topicless copy-cats or freely user-defined communities) are hit-or-miss, I personally don't like them in a federated space unless they are specifically solving an issue.

lemmy.ml is somewhere between topic-based and general. It is explicitly "A community of privacy and FOSS enthusiasts, run by Lemmy’s developers" (I notice that broadened a bit, surprising although no complaints), and you can see that bias in the communities list, but the mods aren't aggressive with enforcing the topic. There are random sports, country and interest communities here. Whether that's out of inactivity (volunteer time and effort is limited!) or lax policy (the more the merrier!), it makes this feel more like a general site despite the tagline. I remember last time I checked (admittedly a year ago) the staff were explicit and purposeful that this is not an official instance and was not trying to cater to everyone as a general instance, encouraging people to make more granular instances for things which weren't meant to go here.

If that is the case (again, policy could be different) then maybe some extra messaging on the Create Community and Register pages could help prevent the regular issue we had when someone fundamentally against the community (like someone kicked from reddit because of racist comments) would show up and be surprised when they were herded out of here too.