My comment related to the ‘Narcissist’ epithet - not so much an Olympic athlete. But - I would assume Rowling would consider a biological male competing against biological women unfair to the women.
It’s not coincidence. Usually the Y chromosome carries the SRY gene, which causes gonadal cells to testicularize and release androgens, which in turn will cause cells to organize in a male configuration. Sex differentiation is almost entirely the result of cell reception to sex hormones.
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Meanwhile, even more studies are reporting that there's no advantage after hormones, so...
https://www.forbes.com/sites/lindseyedarvin/2024/04/25/transgender-athletes-could-be-at-a-physical-disadvantage-new-research-shows/
Rowling considered it unfair that a cis woman that she thought was too masculine was allowed to compete in the Olympics.