edit: on a more serious note, yes, when studying the biology of humans or similar organisms probably 99% of the time you can pretend there are only two genders/sexes, but
that doesn’t make it true
even just 1.7% of the U.S. population is still a pretty big number (~580k people)
Just like humans are born with 10 fingers, Biologically there are only two genders.
Yes there are VERY rare exceptions, but we shouldn’t be building PS5 controllers to cater for people with 12 or 3 fingers.
https://www.playstation.com/en-us/accessories/access-controller/
edit: on a more serious note, yes, when studying the biology of humans or similar organisms probably 99% of the time you can pretend there are only two genders/sexes, but