There certainly aren't '64' genders. That's picking numbers out of thin air on some thin arbitrary justifications.
OK, first we have to address the whole sex/gender thing.
What I mean to say is there aren't 64 sexes.
There aren't two either. The most accurate description would be there are approximately two sexes.
That sounds like splitting hairs, but it's not, it's just a reflection of the true nature of biological reality, rather than the simplified approximation we like to work with most of the time.
No given person matches the ideal of a particular sex. Rather, they match it within a certain degree of tolerance.
Some people, a handful, are ambiguous and cannot meaningfully ascribed a sex, because any category you choose is going to be wrong.
But what does it mean anyway? People these days like to think there's a nice, clear, concrete definition of what makes you a particular biological sex, but there simply isn't.
And even if there was, it's not likely to be one anyone actually uses in practice.
It especially isn't genetics.
You know what it is? It's the penis.
That's all. It's how it's been defined for so long, we take it for granted. And yes, we know new things, such as genetics.
But we aren't exactly performing genetic tests when we write 'M' or 'F' on a birth certificate...
No, we are just going on the medical opinion of a doctor or maybe a midwife, or someone, who will take a quick look at what an infant has between it's legs, and dictate a huge number of things about it's future based on a simple observation.
Simply put, if there's something there that looks like a penis, it's male. Otherwise, it's female.
Even if there's ambiguity, or extra stuff going on, it is still principally decided by the presence and approximate size of a penis-like appendage...
Any other aspect of biology or reproductive capability or stuff like that rarely gets a lookin.
I already laugh at people that argue from genetics just on principle, but this reality really rubs it in.
Still, the unfortunate implication of the logic behind this is that we classify people as male/not-male.
And, that the sole classification of being male, is having a penis, and female actually is mostly just relegated to the label for 'other'.
And indeed, though people are rarely quite that simple-minded, think about how many subtle hints most cultures seem to posses that reinforce the idea that if you lose your penis you aren't a man anymore, regardless of anything else.
Although, this seems to get tossed out pretty quickly if you bring in the idea of someone trying to get rid of it deliberately in order to be regarded as female, but then it really isn't quite that simple of course...
And, even regarding the idea of losing your penis making you stop being male, it doesn't quite reach to the levels of what the male/female classification then would imply. Though it is the underlying logical basis for how we classify male and female, we haven't quite decided to truly treat female as 'other' in the way the means of classification imply.
Which makes sense too, because edge cases aside, there's no reason to consider that a category that excludes males would contain anything other than people who have the identifiable biological features we associate with females.
The rarity of the edge cases means it ordinarily doesn't matter that the practical tool used to decide what someone is does in fact classify people as 'male' or 'not-male', rather than actually bothering to actively try and identify 'female' as well as looking for the one thing considered to define being 'male'...
Still, it's awkward to consider what the actual implications of how we typically decide this actually are.
As for gender, well, assuming we take the definition of it being a social construct (some people try and argue against that definition of the word for some reason), it becomes even more meaningless to ascribe a specific number to it.
Since it contains so many completely arbitrary elements, you could argue there are 2, 3, 64, 500, 5 million, or whatever different genders, and be able to make a viable, fairly reasonable case for it being true.
But just as most of the elements defining these genders would be entirely arbitrary, it follows that so would the exact number anyone might claim to exist.
It's just, kind of meaningless arguing about how many genders there are, because there's not really anything that is objectively meaningful that you can say to prove any given number correct.