It is unclear, partly because no medical diagnosis has been revealed, only speculated. The speculation is a condition that itself is an umbrella term.
Daily Mail report here (excerpts below): https://archive.ph/GvezG
A bit repetitive at times, but I think it covers the background pretty well.

Khelif hasn't yet commented on the subject but speculation abounds that she has a [Difference in Sex Development], a rare condition that only affects between 0.05 and 1 percent per cent of the population.
Also called 'intersex' conditions [...]
DSD is an umbrella term for 40-plus individual conditions which develop in the womb.
For example, a person can be born with female genitalia but have the XY chromosome combinate typical of males as well as internal hidden testicles.
They can give people unusual combinations of chromosomes and reproductive organs, which in the context of sport, can boost their performance.
For example, an athlete may be born with female anatomy but have a DSD which boosts her level of testosterone, a hormone critical to building muscle and strength.
While many DSDs are spotted at birth, some only come to light in puberty or as a result of a medical operations, test and even autopsies.
At the time International Boxing Associate president, Umar Kremlev, claimed the tests had proven Khelif 'had XY chromosomes', which are an indicator someone is male.