But if a CIS female has a different brain structure then gender cannot be a social construct.
So? If the brain of the average woman is different from the average man's, then it's unrelated to gender.
Gender is a social construct insofar that we, as a society, decide to connect certain traits to a sex. High heels used to be worn by men, for example. That's an example of a gender related social construct.
If a transgender male has a female brain he can't be 100% male.
It literally doesn't matter what his brain is like, he's male therefore his brain is male. Period.
There is no "female" brain, that's ludicruous. A brain is not male or female, it's part of you. If you're male, so is your brain. Again, even if he has a brain similair to a women's, he's still male and so is his brain. Every cell in his brain is xy.
Besides, again, this argument doesn't work because the average tranny is a fat anime watching porn addicted loser, a farcry from the average woman. If anything, their brain seems more "masculine". Or rather, "autistic", I guess.