Commenting on this part:
In biology, there are still only two sexes in terms of sexual poles, but biology doesn‘t deny that in about 0.1% of the cases, intersex conditions happen. Some years ago, an intersex deer was found in Germany, exhibiting both male and female outward features, just as an example. Of course, textbooks at school and university only present the typical case and don‘t account for rare variations unless they are for students specializing in that field.
Regarding transsexuality, which is not intersexuality in the original sense of the term, it has been studied by a relatively new subdivision of biology, neurobiology. Neurobiology has come to the insight that there is biological „content“ in the brain as well, and the brain has been ignored as actually being the most important sexual organ.
Of course it‘s not easy to change what people have learnt in centuries, but it‘s definitely possible if they are willing to listen about new science, and I‘m a bit pressing considering how many affected people will throw themselves in front of a train or jump from bridges in the meantime due to rejection by society.