Pseudohermaphrodism exists in humans (people born with multiple sets of genitals). That doesn't fit into your claim of only bimodal and this is just the external presentation of gender. I would encourage you to explore the topic more. It's not as simple as boy/girl only. https://science.jrank.org/pages/3310/Hermaphrodite-Hermaphro...

Bimodal is a case of multimodal where n=2.

And you're going to have to explain why it's a sign of a decline.

Were the Romans thinking it was only gay if you were on the receiving end a sign of cultural strength or decline?

Of course, even though they're one of the more famous cultures to have "declined", that's only if you artificially don't consider Byzantine Rome, and there's plenty of people living in Rome to this day.

Bimodal is not binary. Obviously there are two ‘modes’ - ie peaks in the probability distribution function, male and female, but there’s a lot of overlap in between. The term ‘multimodal’ doesn’t mean ‘bimodal with overlap’ lol, it means that there are multiple distinct peaks in the probability distribution function.

Look up a bimodal distribution for clarification.