The sources people cite for Imane Khelif being biologically male are:

• an opponent with a history of forfeiting after a single punch and claiming after the fact that her opponent was cheating and that was why she was forced to forfeit did it again. When she did that in the past with other opponents, there wasn't any assumption that the baseless cheating allegations were on gender/sex grounds.
• The IBA, an infamously corrupt organisation with the infamously corrupt Gazprom as its majority owner disqualified her from a tournament without saying why. There are enough historic allegations of them disqualifying people for refusing to throw matches that it's plausible that the only reason she was disqualified was that she refused to throw a match they wanted to rig.
• JK Rowling said she looked like a man. She does this a lot with a lot of cisgender women due to internalising unrealistic femenine beauty standards.

People have claimed sex testing was done by an accreddited independent lab, but chasing that citation just leads to the IBA saying she was disqualified without elaborating why, which doesn't support the claim.

There's no actual evidence to support the speculation. That doesn't mean it's untrue, but does mean it's unreasonable to present it as fact - there's just as much evidence for alternative speculation, e.g. that she bribed the opponent to forfeit and was disqualified by the IBA because they found she'd bribed people to forfeit in the past, and it would be just as unreasonable to spread that rumour I just invented around as if it were fact.