That's a pseudoscientific view of sex that is not the understanding of most people, and biologists in particular - who need this concept to cover all anisogamous species.

The sex binary is the only model that makes any sense on this scale. Some people have tried to come up with "sex spectrum" models, but they ultimately fail for being too arbitrarily defined and too anthropocentric.

> Gender is bimodally binary.

This is also far too arbitrarily defined, and attempts to come up with concrete definitions typically just bake in culture-bound sex stereotypes of femininity and masculinity. Which makes it particularly harmful when activists attempt to redefine 'woman' and 'man' in terms of this instead of sex.