You have a sex, which you can't change, and a personality. That's it.
For men, it's usually those who want to go into women's single sex spaces but can't be arsed putting on a bit of lippy (not that that means the lippy men should get in!) So they go "I'm non binary, I'm more comfortable in the women's spaces" and think that gives them rights. It fucking well doesn't.
For women, they're tired of being objectified, the male gaze, porn culture, the pressure to look like you're off to Love Island. So they go "I'm non binary, so non of that awful stuff applies to me anymore". Unfortunately it still does, a sexual predator isn't going to leave you alone because you think you aren't a woman anymore, he won't give a shiny shit.
Both sexes take this shiny new identity and use it as some sort of personality transplant. How do you know if someone is non binary? Don't worry, they'll tell you! 🥁 All of a sudden, they (and I use that word for the group of people) think they're cool and interesting, they can identify as queer too and that gives them the sort of gravitas they never had when they were boring old men and women.
They can sit and lecture you with that smarmy self satisfied smirk they all seem to have, about life being soooo hard because someone didn't use "they/them" at work once, so naturally they dissolved into a puddle of uncontrollable shaking. But once they rematerialised the co worker got dragged into a disciplinary and the whole department had to do a allyship course.
TLDR: Pain in the arse attention seekers.