For the record, the most recent mental health intake I did had "Self diagnosed autism" as an option for existing mental health conditions.

"Mental Health professionals don't support self diagnosis"

Actually, a good therapist will recognize the systemic oppression that can limit people's access to diagnosis. Systems theory would discourage ignoring this. Social Justice Theory emphasizes depathologizing difference.

Many therapists these days view the client as the expert on their own experiences. Many won't even provide an offical diagnosis they could give unless you state you want it.