Ah, if only everything in life was as simple as yes or no, black or white, on or off. What you fail to realise is is this kid will grow up, may eventually take testosterone injections, get hairy, grow a beard, and then end up scaring the women and girls when HE goes into the public toilets you’d have him go in. He shouldn’t have to use the disabled toilets or unisex toilets or whatever the school is calling them, as he’s not unisex or disabled. Like a poster has already said, a wheelchair user needs a well thought out / planned toilet space, which is why although you do get wheelchair toilets in sex segregated toilets, most are unisex.
As for title IX, this is a rule that gets interpreted in all manner of different ways by different people, and really needs clarifying or changing.