Gender dysphoria is a recognized mental illness and is usually the impetus for somebody to transgender. According to the Mayo Clinic, all people who transgender are not afflicted with gender dysphoria, but I would guess that the large majority are. If my guess is right, then yes at least most transgendered people suffer from a bonafide recognized mental illness.
WHO among others cites statistics of a very high rate of mental disorders and substance abuse among transgendered people. Of course in this 'woke' world we now occupy, most say it is because the rest of us don't accept these people as 'normal'. (Every time I hear that I think about the nice assortment of pretty bridges I have for sale.)
I definitely believe a person should have reached the age of majority before having any kind of hormone therapy or surgery to transgender. And I think parents or others who do that to kids should be jailed as should those committing any other form of child abuse.
I believe it is anybody's constitutional right to transgender if he/she is an adult and can find qualified medical people willing to do it. I think ANY medical personnel should be allowed to refuse to do it on ethical/moral principles though.
And while a transgendered person certainly has the constitutional right not to be verbally or physically assaulted, they do not have the right to demand that the rest of us accept them as 'normal' or pay for their considerable expenses to do it.