Polyamory isn't strictly LGBT+ but it's often included in pride posts. I think 1. because queer people are generally more open to it, and 2. because it defies a mode of "normative relationships" in modern western cultures.

I'm not strictly monogamous or polyamorous, but I prefer relationships on the open side of the spectrum. I think anyone who has or wants a relationship that defies current norms gets too much shit for it. I'm not much of a believer in the "nobody wants a serious relationship anymore" thing and I believe even less that poly people are somehow to blame for that. Some poly people are toxic, but they're not toxic for wanting a poly relationship or for proposing it alone.

Just remember that dating apps are not a reflection of your entire dating pool, be mindful of why people use certain apps (don't chase love on Grindr for one) and consider that for every post asking why nobody wants a monogamous relationship, there's TENS OF THOUSANDS of people liking and sharing it, meaning that there are indeed plenty of monogamous dating options you could be talking to!

Long story short: have the relationship YOU want and leave people who don't want that alone. Other people aren't to blame for you being single, nor are you entitled to a relationship in the first place.