You're confusing sex with gender. Both are a spectrum but sex is a biological spectrum of sexual organs in a living creature and gender is a quality, projection and performance of a person that also lands on a spectrum.

The confusion is because they both use male and female but sex and gender are different things. Gender can change throughout a person's life. A person's sex is consistent throughout life and can't be changed. A person's gender can't change their sex. Sex also isn't as simple as xx is female and xy is male, there's a whole bunch of things that can't put a person in one, both, or none of those categories. Gender is even more complicated.