Mosaicism does not mean the person has both functioning testes and ovaries. Gametes, or the potential to produce one or the other type of gametes (in the case of infertility, for whatever reason) determines sex. There are no third type of gamete. There are really great resources out there, both by intersex individuals, and scientists who explain all this. They are constantly dragged into the trans debate, when they don't have anything to do with it. Human sex is not a spectrum, there are no speggs!
It's only not a spectrum because you are deciding your specific criteria and dragging the debate into what is trans or what is intersex when that is not at all what I am talking about.
You are defining an individuals sex based on which gamite they can produce. That's fine if you want to classify them that way.
I'm saying that how a person FEELS, their sexual urges, how they perceive themselves is affected by more than that one ability to produce sperm or eggs. There are a large number of ways the human body expresses it's sex, and a single body can have a mix of these. How they affect their brain and in turn their mind and emotions and feelings is what determines if they are happy and comfortable in their body, or if they feel their body doesn't match with how they feel.
That was the whole point of my bringing up all the various ways a body can be a mix of genders. I'm not saying that there is a specific 3rd gender, I'm saying that some people have a mix of both and how they feel about themselves might not match how YOU feel when you look at their physical body.
Everyone saying there is no 3rd sex is missing the point. People can be a mix of the two, and that can cause them to want to change their body to match their mind. They can have biological reasons for this, they aren't all just brainwashed into a fad. And if a fully male adult wants to wear a dress for no other reason than they like to look pretty, that's ok too.