An article in UnHerd by Mary Harrington reviews two books on the subject:
"Lars Horn's 'Voice of the Fish' and Travis Alabanza's 'None of the Above' attempt to define the idea"
I can't actually read the full article as I'm not registered but I gather the concept is all a bit vague and hard to pin down. The comments though are interesting and well worth a read as they range from anecdotes to the blunt "why would anyone want to publish this tripe" (i.e. the books, not the article) to wrestling with trying to understand and account for how all this came about and pointing out various conceptual contradictions and that post-modernism itself doesn't believe in identity. One woman noted that her daughter has 'a change student' in her class. Interesting term, I thought. Haven't seen it used before.
unherd.com/2022/08/what-does-it-mean-to-be-non-binary/?tl_inbound=1&tl_groups[0]=18743&tl_period_type=3&mc_cid=8b3aac03ec&mc_eid=31e133b3a4