There are only two genders. Man and woman. It is not a choice. You either have a todger or you don't I'm afraid - but feel free to dream.
I understand why a lot of conservatives push back against the idea of infinite genders as a denial of reality. I think gender theory made a big mistake in repurposing the word "gender" so that it's no longer synonymous with sex.
There are only two sexes- man and woman- and your sex is determined by your chromosomes/genitals. Of course, intersex people exist, but I don't think that changes the fact that there are two sexes any more than babies born with 12 fingers changes the fact that human beings have ten fingers. You're talking about sex here, and I completely agree with you there.
However, the word "gender" has been redefined to mean gender expression/ gender roles. There are infinite ways to express your gender, which is where the idea of the gender spectrum comes from. Some girls are more feminine than others. A tomboy would be someone with the sex of a girl and the gender of a boy, as they have a female body, but take on a male role in society/ present themselves in a masculine way.