I'd like to talk about Xenogenders for a second.
I genuinely have no idea why someone would describe them as fullblown mental illness, that's just a wholly unwarranted overreaction.
that said, on the rare occasioan where someone bothers to actually list any of them out with names and descriptions, it usually reads to me like they're just deliberately splitting hairs to artificially lengthen the list for it's own sake. This video for example lists two genders that are literally just different ways of phrasing the concept of being undefined.
Furthermore, picture your favorite xenogender for a second. Imagine you met someone who met it's description perfectly... but who still identified as simply a man or woman. The way I see it, either their identity is invalid, or the gender is. You can't have both.
All an all, a perfect example of the problems that arise when you treat being LGBT as somehow inherently meritorious rather than just another state of being.