I’m happy to give you the benefit of the doubt on the second apology, but perhaps I can speak to the subtext here that you are struggling with this issue because you’ve bought into the oft-repeated fallacy that it’s “basic biology” that trans people are not “really” who they say they are.
I’m an actual biologist, and this is false.
You are correct that in humans male/female differentiation is determined by genes on the Y chromosome. But there is very little information on the Y chromosome, it’s tiny, and mostly junk. What it contains are high-level “triggers” that set in motion a whole chain of complex events. All the many genes required to make every part of a human of either sex are on the other chromosomes, and present in all of us. To put it crudely, every human being contains all the genes required to make a penis and to make a vagina; we just do one or the other according to which pathway is triggered.
Now consider that this also applies to the brain. Our brains (behavior and feelings) are also sexually dimorphic to some extent - men and women are different. Of course, it’s highly contentious just how much of the difference is genetic, and it’s hard to distinguish between things that are genetically determined and things that are somehow “firmly established” early in life. But there’s some difference, including how we feel about ourselves, our sense of who we are - our identity. But just as with a penis and vagina, all the genes to make either a “male brain” or a “female brain” (nobody knows exactly what that means, but it means something) are in all of us. And the brain that actually develops just depends on which pathway gets triggered.
From a biological point of view, then, the hypothesis to explain how a trans person comes about is obvious. Something unusual happens in the process of determining which developmental pathway gets triggered, and it goes one way for the brain and the other way for the rest of your body. And again - this is biologically perfectly plausible because we all contain all the genes required to make any part of a man or a woman, including the brain.
The evidence that something like this actually happens is simply the existence of trans people, who have always existed throughout history, and most of whom are insistent and persistent about their identity despite appalling treatment by society. Why on earth would anyone assert a trans identity unless it were real? Brains are just as much part of our objective physical reality as our genitalia, and although we can try to change some aspects of how we feel and how we behave through personal development, we cannot change or choose who we are.