Except it is. It *exactly* is. You claim its fundamentally cellular. In that, you are right. But you’re wrong about the genetics of it being simple.

In the medical journal "Frontiers in Neuroendocrinology" in the research by professors Roselli and Balthazart, Volume 32, Issue 2, Pages 109-264, April 2011, they identified is not the X vs Y chromosome that determines gender/sexuality, but a wide variety of genes. The reason for this prior misconcrption is the SRY gene on the Y chromosome plays a strong role. However, it does not exert absolute determination. There are well over a dozen genes spread across the genome, each with a multipliciltive effect on outcome and a different effect, meaning that from before the dawn of civilization, humanity has had more genders available to it than there have been people born to date; effectively meaning it is scientifically proven that each person is entitled to their own unique and distinct gender (and will be for many many generations to come until we exhaust all the potential gender combinations... which will take more time than the time it will take to evolve new genders, so effectively limitless.)

And every medical field is in agreement (at least in countries not exerting political power to subvert the scientific process for politics, such as Russia and Pakistan), of the multiplicity of gender.

As far as your concern transgender people may be lying, that’s silly. Liars lie for the purpose of gaining advantage. The disadvantages of being transgender faaar outweigh the advantages. Not the least of which being many people in the world actively targeting you for aggression or extermination. Considering the drawbacks, the only reason that really overpowers them is not to live a lie your whole life.

https://www.sciencedirect.com/journal/frontiers-in-neuroendocrinology/vol/32/issue/2