What do you mean There are only two genders. Change my mind ? I dont understand.
Change my mind is a format some like to use when discussing a position that some consider to be ill informed or outrageous. "This is my position, I know you may no like it so make your case as to why I am wrong" being a fairly good alternative phrasing.
As for two genders then as I understand it then it has two main paths.
1) Some people use it as a shorthand for denying the need to acknowledge aspects of transgenderism/transgender individuals. This breaks down several more times as there are a lot of aspects to the debate for some people -- some simply mean it as a statement that transgender does not exist, others would say it does exist but then have other thoughts on how one should approach it.
Others still would take other paths that others find very odd and also appear to fly in the face of generally accepted biology, medicine and observed reality.
2) There are some people in the world that like to say there are basically infinite genders.
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I already went with my thoughts on the matter as a whole (
https://gbatemp.net/threads/there-are-only-two-genders-change-my-mind.502144/page-5#post-7939807 ). Though for the sake of the simplistic thing I would say there are two genders, and I don't care what your head reckons it is and whether that matches the genitals you were born with.
The people I was referring to in the latter part of 1) would typically be called social constructivists. They often say that sex and gender is a thing made up by man and thus can be anything you want it to mean, this despite clear and observable traits wherever you go in the world, however far removed different humans are from each other, regardless of whether you find some isolated tribe in the jungle or someone in a big city, whether you look at babies that can't know anything, whether you look at animals, whether you look at edge cases (damaged genitals), when you throw around hormones into people and observe the results...
It gets even more fun if you want to consider history -- old school European aristocracy had high heels as the height of fashion for men, long nails have also long been a sign that you don't have to work with your hands, some would tell me that blue and pink swapped as the colours for a given gender at one point. Yet today they are what they are with regards to being associated with a given gender.
For 2) then I quite like the following video for highlighting how ridiculous it can be
If you want to box up aspects of your personality and give it a proper noun then so be it. Why I would care to have it supplant or basically render infinite and thus unknowable the otherwise useful concept of gender I do not know.