See here...
Up until 2019 the WHO classified transgender people with a mental disorder.
WHO Drops Being Transgender from List of Mental Disorders | Time
Also have you ever heard of the Diagnostic and Statistical Manual of Mental Disorders(DSM-5)
What is the Diagnostic and Statistical Manual of Mental Disorders(DSM-5) used for?
The Diagnostic and Statistical Manual of Mental Disorders (DSM) is the handbook used by health care professionals in the United States and much of the world as the authoritative guide to the diagnosis of mental disorders. DSM contains descriptions, symptoms and other criteria for diagnosing mental disorders.
What book provides for one overarching diagnosis of
gender dysphoria with separate specific criteria for children and for adolescents and adults?
The DSM-5
Psychiatry.org - What is Gender Dysphoria?.