I’m not someone remotely into that market, but my understanding is there isn’t a huge demand for this outside the Ashley Madison type who are cheating. The various cliques have their own methods of finding each other and generally aren’t interested in broadcasting that to a wider market.
A lot of the polyamorous people I know are on the apps or have tried them, but aren’t happy with them. Partly because the apps generally aren’t good, and partly because you end up with a lot of wasted “your desired relationship structure isn’t what I want” matches.
OkCupid has some support for it, but that app hasn’t been good or interesting in years. Tinder lets you pick your relationship type, but you can’t like filter by it. Soneone threatened to “report me” on Hinge (I think?) for wanting a non monogamous relationship. Maybe they thought relationship anarchy was something dangerous.
This might be different outside of NYC, where I am.
