There's not even a single universal way to divide sexes into two absolute sets with no overlaps or outliers.
FEmales are those whose reproductive anatomy is arranged around the production of ova and the gestation of offspring, even when some of that anatomy is misformed or absent, and even when ova are not actually produced.
Males are those whose reproductive anatomy is arranged around production and delivery of sperm, even when some of that anatomy is misformed or absent, and even when sperm are not actually produced.
Two genders is an approximation.
"Two genders" is a result of eons of sex-based discrimination which grants social privileges and agency to males, and which places females as subservient second-class citizens.
Two sexes is also an approximation
Two sexes is the actual reality of sexually reproductive species on this planet. It's not an approximation - there is no third sex among any mammals, nor I believe (would have to double check) among vertebrates. Some algaes have more than two sexes, but they can only combined to reproduce in couplets - as long as the two gametes are not the same type of gamete, reproduction is possible. But among mammals there are ONLY two sexes, and hence, there are only two sexes.
This is how sexual reproduction works. In the real world, in reality. Evolution does not give a fuck about people's feelings, and it does not care whether we "like" the sex we developed as. Sex isn't an option that anybody gets to choose, and it's immune to wishes. Sex is real, it has real impacts on people, and it is strictly binary.
Anything else is anti-scientific nonsense presenting wishes as if they were facts.