I find it so interesting that gender incongruence is no longer classified as a mental disorder—gender identity disorder—by either the DSM-5 (2013) or the ICD-11 (2022), even though it is clearly a case of someone's internal state (their self-perception) not aligning with external reality (their sex at birth). What is that if not disordered thinking? If I believe that I am Elvis Presley but reality evidentially says otherwise, is that not indicative of a mental disorder? Traditionally, psychiatry defines a mental disorder as a condition in which internal states (beliefs, perceptions, or identity structures) are discordant with external reality or cause functional impairment. Under that rubric, delusional misidentifications, body dysmorphia, and anorexia nervosa are classified as disorders precisely because subjective experience conflicts with the body's objective condition. (See note at bottom.)
The DSM-5 (American Psychiatric Association) and ICD-11 (World Health Organization) committees did not 
discover that gender incongruence is no longer a mental disorder, they simply 
decided it should no longer be classified as one. Why? There were no new biological or psychological discoveries that would warrant reclassifying the diagnosis on evidentiary grounds. Instead, both said the justification was driven largely by sociopolitical and ethical considerations pertaining to social impact, stigma reduction, and human rights. 
The APA said they changed the DSM for reasons pertaining to social impact—because how it defines and diagnoses mental disorders "impacts how people see themselves and how we see each other" and can have a "stigmatizing effect" (2013, 
PDF). That really seems unrelated to diagnostic and clinical care. The WHO was even more explicit, saying the revision in the ICD was intended to avoid "labeling transgender identities as mental disorders," citing advocacy pressure from "a range of civil society organizations as well as the governments of several Member States and the European Union Parliament" (
2016). The intersection of stigma and mental disorder diagnoses creates unique burdens, the WHO said. This is political and advocacy pressure related to legal status and human rights, not scientific or clinical evidence.
-  ICD-11 = International Classification of Diseases, 11th revision (effective January 2022).
 
-  DSM-5 = Diagnostic and Statistical Manual of Mental Disorders, 5th edition (effective May 2013).
 
Note: It is dangerous to privilege inner self-conception over empirical embodiment. It is also why there is an overt asymmetry when it comes to so-called "conversion therapy." In contemporary policy, "conversion therapy" is defined as any attempt to change a person's internal life to align with external reality. But the same conceptual structure is not applied in reverse: Efforts to align the body with the self-perception—through hormones, surgeries, or social transition—are not defined as "conversion therapy," strangely enough, but as "gender-affirming care." It is a one-way street, an asymmetry that is ideological, not medical. It arises from the normative presupposition that internal self-identification is authoritative and external reality is subordinate and mutable. (Our narcissistic tendencies are pervasive and going unchecked.) For no reason that makes any sense to me (beyond spiritual rebellion against God), altering the body to match the self is deemed therapeutic, but altering the self to match the body is deemed coercive.