Not just that, but it fits the one of their beliefs: sex and gender are two different things, and would be completely unrelated if society didn't socialize each sex into one particular gender. So, they point to transgender people and say that this is proof that their hypothesis is correct.

However, this ignores one key piece of evidence. In every human society, masculine males (to use their term) and feminine females have been the norm, even in societies that have some kind of transgender or nonbinary role. The probability that this would happen by chance are vanishingly small.