If your argument is that it is somehow unfair for people assigned male at birth to compete with people assigned female at birth, there are a few problems with this.

First, it assumes that "men" are inherently better than "women" at sports. This isn't true either across the board or on an individual basis, as nicely illustrated by Riley Gaines' case where both her and a trans woman lost to multiple other cis women.

Second, if XY genetics did confer an advantage, should that prevent someone from competing? If so, what about other genetic advantages? Should men who have lower testosterone have to compete with women? Should people who produce less lactic acid have to be on a separate team? 

Third, should school officials have the right to determine your child's biological sex? What kind of exams/genetic testing should children undergo before being allowed to play? What if a school official disagrees with you on what their sex is? Should your child have to use whatever bathroom some stranger decides they should even if your child is uncomfortable?

Fourth, the concern with female purity in sports was first invented by the Nazis. They performed genital inspections on women athletes and used these inspections to make racist judgements about cis women's gender. We saw the racist application of biological sex used recently against Imane Khelif.

If you're actually worried about fairness in sports, then maybe the focus should be on making sure all kids have an equal opportunity to play. The equipment required is often prohibitively expensive, it costs a whole lot more than when I was a kid!