Biology isn’t that simple. A person can have one fewer sex chromosome, monosomy, one extra, trisomy, and many extra, polysomy. In fact it’s starting to show that a significant minority of people have trisomy 47 (the name for having one extra sex chromosome) but live perfectly normal lives because those extra genes are suppressed. You could have an extra x chromosome and never know it, does that exclude you from being a man or a woman? Which brings up the topic of gene expression and epigenetics which is even more complicated. If you’re looking at science to give you a certainty about sex and gender you’re in for a long search.
That’s the extreme minority. To keep things simple let’s just say xx one bathroom and xy the other. That encompasses 99.9% of bathroom usage. For the cases you are talking about I’m sure that person can figure out what bathroom to use for themselves and explain it to anyone that asks.
Nah. That’s just sex.
But there’s been long proved that what we call gender is not 100% defined by sex.
For instance, our traditional gendered bathrooms. The concept does not work if we just take sex into account. As the reasons we have for segregating bathrooms in genders does just not work if people have a different presentation, external sexual characteristics or behavior, that it is traditionally assumed for one sex or the other.
To put intro crude words. Women that would like to have a women exclusive bathroom would really not be happy if someone walks into that externally looks and behaves, and even have the sexual characteristics of what they perceive as a man. It would not matter if that person would have XX instead of XY.
That’s the extreme minority. To keep things simple let’s just say xx one bathroom and xy the other. That encompasses 99.9% of bathroom usage. For the cases you are talking about I’m sure that person can figure out what bathroom to use for themselves and explain it to anyone that asks.