I’d call that a “webpage” though, one with an ill-fitting name. One person with a sandwich board and a megaphone yelling at a few passers by who at best smile, give a half-hearted thumbs up, then walk away.

To me, for it to live up to the name “community” that implies several people sharing stuff and a bit of reciprocity.

Of course that might take time, the first poster might be one of those proverbial people planting those trees that they’re never going benefit fron the shade of. Theres no harm in just creating it making a few posts and leaving them there- it might become active eventually. But it could be never and it will inevitably take a lot longer if the platform only has a million users a day total than if it had a billion.

You can probably do some sort of critical-mass / chain-reaction / markov chain type model to get a handle on the chances of a niche community becoming active in small population. Like that ‘Drake equation’ for trying to stop people wasting resources on SETI.