You need to read up about XY 5-ARD (the condition Caster Semenya has and Khelif surely has). Being XY with active SRY means you're male. Khelif has admitted having the SRY gene (in an interview with L'Equipe). Males have very significant advantages (50% plus) in power sports such as weightlifting and, yes, boxing.

Sex isn't "more fluid". It's entirely binary, but DSDs (differences of sexual development) can make appearances deceptive - so an XY male can be wrongly recorded as female at birth, especially in countries with inexperienced medics and midwives.

Phelps's records have all been broken. By other males, of course - no female is getting close to his numbers. That's male advantage in action.