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.

The current doctrine is that there are unlimited genders, if you can think of one you can call yourself that, they call them "neopronouns" and aren't simply relegated to xe/xer but include things like wolfkin and dragonfucker. There's also plurals which to the best of my understanding feel like there's multiple people usually with multiple neopronouns inside their head simultaneously.

I'm not either of these so maybe someone who is can elaborate better, but that's what I've been told and I hope it helps.

Fear not I, a still rather confused individual, but with slightly more knowledge on the topic shall answer thy call (I seem to suffer from the curse referred to as "being genderfluid" by the scholars of that gender stuff)!

Somebody who is non-binary is just someone who does not feel like they are entirely male or female. This can mean that they are both, neither or a different gender not connected to either but also not entirely absent or of course any combination of the previous examples.

In my case (genderfluid) I just flop around on the gender spectrum, mostly not having a gender or feeling a bit feminine but sometimes I do feel male or like some other gender. Though genderfluid just means that the persons gender changes over time, it doesn't have to be the same genders that I experience.

Hope this helps :)