Not to nitpick but to me the title of this post is implying that XXY individuals are born female. Generally they’re born male.
What the comment is referring to is likely Swyer Syndrome, where the individual has an XY configuration but a dysfunctional gene in the sex-determining region of the Y chromosome. This means the embryo develops female anatomy and the resulting children tend to identify female, but they lack functional gonadal tissue. It’s estimated to occur at a rate of about 1 in a 100,000 females.
By the by, treatment for these individuals usually involves removing the dysfunctional gonadal tissue as it often becomes cancerous (which often gets misunderstood as “gender reassignment surgery”) and supplemental hormone replacement therapy. They would be affected too by any bans on hormone administration to kids often connected with trans people. One of the reasons why blanket bans should be a no-go regardless of how you feel about any other trans issue.
WadeTheWizard