And that's exactly what's being discussed in academia right now. Sex is a concept, as well! Classic example, but just think about seahorses. The "men" are giving birth to the living children. Are they any less "male", in terms of the concept we know? No. But doesn't our concept state that only "biological" (/cringe) women can give birth? Then isn't out concept simply—wrong?
It's super complex, and I admit that it's not easy to understand that even the "biological sex" is a concept that we made up based on superficial criteria such as penises and vaginas. But based on different manifestations of chromosomes in human bodies—and the fact that the brain can have different chromosomes than the genital area—we can rightfully claim that gender is, in fact, just as biological as the concept of "sex" we have imposed on ourselves.
That doesn't mean that any differences are denied. It just means that the concepts are evaluated in terms of their restrictions to cis and trans people alike.
But, as much as I'd like to, the sources are anything but accessible outside of academia. You just will have to research that if you wanna dive deeper into that topic, and hopefully come across trans scholars and biologists who know what they are talking about—and know how to interpret it.
The barriers to all this knowledge are huge, which is a problem if we ever plan to help everyone accept different concepts (and the discussions around them). >_>
Oh, one more thing, about sexuality:
You didn't, but society does so on a regular basis, which results in (straight) parents panicking over their kids getting sex education, even though it has been shown to be advantageous even at kindergarten age.
Education like that should not fall into the parents' hands. There are too many ideological or religious barriers involved, especially in countries like the USA or, say, Russia.
Uh... I think I covered everything? I hope? I'm half preoccupied over here. xD