The United Kingdom's Prime Minister, Rishi Sunak, speaking at a Conservative party conference, opined as follows.
"We shouldn’t get bulled into believing that people can be any sex they want to be. They can’t,” Sunak told the audience, which applauded in response. “A man is a man, and a woman is a woman, that’s just common sense."
If someone believes they are Napoleon, they are delusional. Those who believe they are a gender that doesn't agree with their physiology are also delusional. Either way it is mental illness.