Finally it’s our turn to play dumb and go “Naah, I don’t believe he meant it this way, we can never know for sure, can’t read his thoughts …”

I honestly don’t understand. What does define the sex biologically? The genitalia, then? I always understood positions like William’s like “XY is the biologically male sex by definition, if the human develops female genitalia and feels like a woman they were biologically speaking still intended to be a man.” I don’t understand what else there could be on an elemental level to biologically determine the sex.