The problem is people in their rush to try and pretend there's more than two Sexes misunderstand something fundamental.
No matter what there is still two Sexes, even if a person has more than one sex or has no sex. A person who is born one sex and transformes into a second sex later is still either male or female, there is no third sex. A person who is genuinely both sexes is 2 sexes, male and female, they are not some different third sex. a person who is androgenous has NO sex.
But in all those cases, there's still just two sexes. So you might say that in some cases people can change sex, or have two sexes, or no sexes.
But there's still just two sexes.