First, let me reassure you that it is NOT extreme to be a lesbian. Being monosexual is NOT wrong, nor is it hateful or bigoted. Your sexuality and lack of interest in biologically male bodies is perfectly okay. Would you call a straight man that doesn't want to suck a dick extreme?

For the poly stuff, I always put in my profile that I'm NOT interested in a poly relationship. Most of the poly people I've met are very up front about it. The three way people also tend to be relatively up front, in my experience. I also talk to women for a while before I'm comfortable meeting up, which couples looking for a quick bang wont be into lol.

As far as trans women / nb bio males, I think it's a combination of stuff. Jawline like you mentioned, but I try to look at a variety of things. Height, overall body shape (are their shoulders very broad), hand size, voice, how they act, how they view women and lesbians in general. Women might be tall, or broad shouldered, or have a deeper voice for a woman, but when you look at the whole picture it's usually apparent.

I always talk on the phone before a first date, and I always meet up in a very public setting. I also sort of see the first date as sort of like... just hanging out with someone to see if there's a spark. If my date turns out to be a trans woman, I just try to have a nice chat to see if we can be pals, same as I would do if I lost interest for any other reason (besides if someone is just... unpleasant and disrespectful).

The way I see it, I can still have a conversation about a topic of mutual interest with someone I don't want to sleep with. Most trans women that I've met irl aren't the totally insane TRA types. I may disagree with them on sex and gender, but I can chit chat about how much of a pain in the ass macarons are to make without accidentally sucking a dick. Meeting up in public helps with the safety / strength differential factor as well.

I also specifically avoid telling trans women and NB Males that I'm not dating them because of their biological sex, because I worry about their responses. I usually just say that I didn't feel like we had the vibe I was looking for, or something along those lines.

Lesbians exist! We just tend to end up in long term relationships pretty quickly so aren't generally on the market for long (unless we live in small cities with tiny dating pools and have to drive 3 hours for potential dates... boooo). Being a lesbian can be lonely sometimes, but we exist!!!