It's not true that "sex in humans is bimodal." Human sex is binary.
What's bimodal in humans is the distribution of certain sex-affected traits and secondary sex characteristics that develop during and after puberty of adolescence. Such as height, size and shape of facial features, amount of breast tissue and facial and body hair, how deep the voice is, whether there's a profusion of extra thyroid cartilage - and how much - on the front of neck over the larynx, and so on.
You're right that being able to produce sperm or eggs isn't what makes someone male or female. Whether humans are male or female is determined by whether they went down the male developmental path or the female developmental path starting very early on during gestation in utero.
At 6-7 weeks of gestation, humans on the male path will develop male gonads, testes, and if development proceeds normally, their testes will eventually be able to make mature male gametes, sperm, later in life starting at puberty of adolescence. Those on the female path develop female gonads, ovaries, and if all goes right, their ovaries will have capacity to generate and release mature female gametes, eggs, for about 40 years between menarche and menopause.
Every once in a while as individuals proceed along the male or female path during development, glitches occur that cause them to have sex anatomy and/or physiology that is atypical for their sex. Aka disorders or differences of sex development.
But with the exception of the teeny-tiny number of humans with two vanishingly rare DSDs - gonadal dysgenesis and ovotesticular DSD - everyone with a DSD still has either male or female gonads, testes or ovaries, and distinctly male or female genetics. In fact, most DSDs are sex-specific, occurring only in one sex or the other.
All the DSD athletes like Semenya, Niyonsaba, Chand, Mboma et al whose participation in women's and girls' sports is so contentious have testes and DSDs that only occur in males. These athletes' atypical male sex development makes them a bit different to other males in terms of how their external genitals appear and work, but it doesn't make them partly female. Like nearly everyone else with a DSD, they aren't in between the two sexes, a combination of the two sexes, or an additional sex.
Claiming that people with DSDs aren't male or female stigmatizes and others them. Calling them the misleading term "intersex" just spreads more confusion about their widely misunderstood medical conditions too.
BTW, the definition of sex that's based on the potential capacity to generate either sperm or egg is the one biologists use for all sexually-reproducing species. Since your view is that "it's a bad definition," I hope you'll share the presumably far better definition you've come up with.
