As a famous meerkat once said, 'Simples!'
Contrary to what some people like to claim, human biology isn't that complicated, sex is binary, and screening for XX and XY is straightforward, non-invasive and any 'edge' cases can be dealt with individually, as duc748 suggests.
The likelihood that people with the tiny number of 'edge' chromosomal conditions are going seek to be Olympic athletes is very small - one of these conditions causes weakening of the bones, so we can exclude them from women's boxing for obvious health reasons.
..people with sexual characteristics that do not correspond to the traditional definition of their gender, and fall outside a binary classification – at 1.7% of live human births. Le Monde.
Is that the 'intersex people are as numerous as red-haired people' nonsense again??
It's so frustrating that no matter how many times dodgy stats are definitively disproven - oh look, there they are again, being presented as scientific fact, and in a reputable newspaper, too.
Head/brickwall interface😡