Biological sex is complex, messy, overlapping. There is a ton of evidence of this, and only someone with Trumpian levels of ignorance can attempt to deny this.
The term ‘biological sex’ is outdated and needs to be thrown out, along with other outdated concepts that we as a society have ditched. There have been numerous historical parallels, where other areas of complex variation were overly simplified and fixed, usually to enable those with more power to use rigid categories as a way of policing and controlling those with less power (rigid class and
race categorisations spring to mind).
A binary understanding of biological sex is a simplification that causes harm to those for whom the multiple components and processes contributing to sex differentiation do not all neatly align. This includes people who are intersex and trans people.
Being trans is not a choice, there is a biological underpinning of being transgender.
We can find a way to live within a complex messy world of biological diversity whilst providing dignity and respect to those who are in a minority.