I’m not sure if I’m understanding the question entirely. Like, if sex is defined by gametes, which I think it is, there are only two types of gametes and nothing in between them. It seems like that has to be binary rather than bimodal. I don’t think gametes can be a result of dimorphism either because they are very different even apart from size. I’ve only heard dimorphism used to refer to traits. Traits among females and males are a distribution with a lot of overlap though so maybe that is what they are getting at. Those traits aren’t sex though. Plus, many of those traits can be changed and do change throughout someone’s life (to varying degrees). For instance, characteristics of my body include breasts and a vagina (or at least something like one 🤷‍♀️), but it is still a male body because I was born male, just not a typical one. Like, using sex to describe someone can be less useful in those situations, but that isn’t a reason to try to pretend sex is something other than what we’ve known it to be throughout human history. 100 years ago, no one had any trouble knowing who was and wasn’t supposed to vote or who the 19th amendment was for. It’s silly we’re pretending like it’s complicated all of a sudden.