I’m not talking about people claiming a brain body mismatch, I’m talking about this idea that gender and biology have nothing to do with each other is something that has become popular recently.
Nobody, including myself, is saying that gender and biology have nothing to do with biology, because psychology largely is biology. The operations of the brain are biology. The operations of how our hormones, physical and mental security effect our thought processes and behavior is biology.
Are you saying trans women have a higher proportion of gray matter in their brains? And trans men have a higher proportion of white matter?
No, as I said before the gray matter/white matter discrepancy is a misnomer due to an average of sizes. Not something intrinsic to male and female. Cranial cavity size being the biggest determining factor of proportional gray and white matter.
If you want to see what actual brain differentiations have been seen, those links talk about it in great detail.
Autistic people do not self diagnose (so they can diagnose autism via other methods); trans people do.
Autistic people self diagnose all the time, because accessibility to autistic specialists especially for adults is extremely skim here in the US, and there's a number of hang ups in taking women seriously within the autistic specialty since their socialization masks their symptoms differently than men. Lastly, there's a number of targets put on your back with official diagnosis, with some countries not allowing autistic people to immigrate, certain adoption agencies or other organizations screening against autism, etc.
But more importantly, trans is not a diagnosis, gender dysphoria is. You can be trans without gender dysphoria, but to get treatment for it you'd get diagnosed by your providing therapist. And, just like with autism, it's diagnosed by meeting symptom criteria which is given verbally or written by the patient.