Presumably you're specifically thinking of 46 XY 5-ARD, which is the DSD that is causing all the contention in women's boxing, running and football (plus no doubt other sports).
This is a male only DSD that is most likely going to be impossible to spot at birth. As a result of this DSD, the scrotum and penis won't form until puberty. For some, their testicles will remain internal. Because of the order in which reporoductive organs form in development, the external genitalia will look indistinguishable from female genitalia until puberty, even though all the internal male plumbing is there.
This DSD must be devastating for those who have it. Thankfully it's rare. Although there are pockets of the world where it is more prevalent (though still rare overall), such as here where it is "common" enough to be given the name guevedoces, which means "penis at 12":
https://www.bbc.co.uk/news/magazine-34290981
So what's likely to happen in pretty much every case is that a boy with this DSD will initially believe himself to be a girl. Then during puberty he'll discover his sex.
Unfortunately for society, sometimes males with this DSD will fly under the radar in sport and will compete on the female passports/birth certificate that they were issued when it was understandably assumed that they were girls.
I should imagine most boys with this condition would want to be tested when they started to experience the confusion and distress of unexpected male puberty at about age 13. Some may end up being coerced into women's sports. Some may see the opportunity of women's sports all by themselves without the coercion.
Regardless, the dystopian situation where anything that is related to being male or female requires genetic testing won't happen.
If you're really curious about how much people on this board know about DSDs, it's worth reading the boxing threads from the summer. Clue: the answer is lots.
I'm not going to join in with the thought experiment any more though.