The American Psychiatric Association and the DSM-5 on gender dysphoria: https://www.psychiatry.org/File%20Library/Psychiatrists/Prac...

Notable points: Gender nonconformity is explicitly not a disorder. Gender dysphoria is, but only in "the presence of clinically significant distress associated with the condition." Approved treatments for gender dysphoria explicitly include "transition" and "hormone therapy, related surgery."

The other major classification system, the United Nations World Health Organization's ICD, has similar language. Feel free to look it up.