Hi Kady, I then don’t know what exactly we are arguing about. Trans people do exist though, and clearly you agree that gender dysphoria also exists. I can agree that the brain scans offer evidence but not proof.
I’m glad that you pointed out the depression and other things don’t have concrete biological diagnostics. However there are countless psychiatric condition such as depression that have detailed specific diagnostic criteria to legally have a diagnosis of such. This includes depression as you mentioned, anxiety disorders, bi-polar disorder, autism, schizophrenia, narcissism, and other conditions. These conditions are clearly very real.
Schizophrenia for example, also has evidence via brain scan that shows schizophrenic brains are wired differently, but no one uses brain scans to diagnose the condition, they use criteria from a strict psychological diagnostic list and are trained to do so. The same for other conditions I mentioned above. They don’t use brains scans to diagnose them, but they are still very real. Instead they use specific criteria in certain ways as determined by psychologists.
In order to receive care such as hormones, surgery, legal name change and gender change, a trans person has to actually get diagnosed as trans gender by a psychologist, doctor, or other medical professional, just like the above disorders, with specific and detailed criteria.
https://psychiatry.org/patients-families/gender-dysphoria/what-is-gender-dysphoria#section_3
Now I don’t consider being a trans a mental illness, but it is a phenomenon that happens in a persons brain, so that’s why it takes a doctor or psychologist to do all of this.
True, some people figure out they are trans to deal with their dysphoria, and then go to the doctor for confirmation. That is generally how it happens. But that also happens for other conditions.

For example, I myself have long known I suffered from ADHD, and often told people that. It was only last year that I saw a doctor and after several intense tests, she confirmed I do have very intense ADHD. I would not have been diagnosed if it weren’t for knowing myself already.
Of course no one has the right to just ask each individual if they have been diagnosed with gender dysphoria by a professional and question if it’s real or not for that person. Is it really our job to do that? Or can we just assume it’s their business if they have seen a doctor about it and gotten a formal diagnosis and started strict treatment. Why delve that deep into someone else’s personal medical history and question their diagnosis? When someone tells me they have bipolar disorder, I don’t go about wanting to know if they talked to a doctor to prove it, I just assume they have.
I will admit it’s not nearly as black and white, psychological criteria for psychiatric conditions vs getting a biopsy or detaching a virus, but it is the system we have.
I have enjoyed discussing this with you. Best of luck to you.