Mostly just in dating apps. Maybe it helps that in in a relatively large city, but Tindr and Grindr usually have plenty of other poly people. FEELD seems pretty feared towards polyamory.
With feeld, as a guy who doesn't date guys, I get about one match every 3 months. About 80% of them are immediate duds. 10% turn into dates like regular. And the last 10% immediately go to "let me show you my tits".
It has been a weird experience.
The two successful dates I got from there were people that were very proficient as polyamory, though.
I kind of struggle with this. Feeld has really been the only positive source of ENM connections in general, platonically and romantically, which is kind of what I'm looking for rn. I recently moved and I wanna build friends and a support network, but Feeld not exactly designed for general connections, it's very slow.
I found a local meetup just recently, I guess my hope is that will help!
So I suppose my suggestion is try feeld if you haven't already. It's got a lot of great people in my experience but it's very buggy
Various caveats apply, ymmv, etc. There is a significant overlap between Poly, and pagans, furries, kink, leather, gamers, programmers, queer folx in my experience. I suspect others could add more demographics to the list. I've found that going to pagan gatherings has been a good way for me to meet like minded people, which can evolve towards relationships of various sorts. I'm not much one for dating apps, I could tell you a few, short, unsuccess-filled experiences. But that's me, and I'm sure if I put some more energy into it, other results would accrue.