Those saying you can’t change your sex because of biology are right when they put it like that. But they are creating a strawman, as Trans is about gender, not sex.
Problem here is that the two words are used to mean the same thing which in today’s society they do not and that confuses the hell out of everyone. In my view men are males and woman are females. If you want to them to mean something else then you are going to have to refine what man/woman means. Good luck without using sex as a descriptor. That being said if you want to call yourself doris when you used to be dave and live like a woman or vice versa (what ever living like a man or woman is) go have at it and be happy. you will still be the sex you have when you were conceived and we split sport in to male and female categories. The wording has to be more specific because of the above mentioned change in what a man/woman means these days. So no strawman at all if you use the correct terms.
If you stick to only females can compete in female races then there is no ambiguity and no one can complain about it. Male/open category as well keeps everyone included and fair.