The fact that laws often define terms does not justify a law defining sex or gender. There’s nothing implicit to concepts of positive law or legislative authority that require legal definitions of gender.
There are so few occasions in law where it’s not a violation of equal protection to discriminate on the basis of gender that there really is almost zero need for law to define it.
Most of those rare occasions are related to reproduction, and even then there’s no inherent reason to define genders, the law could just refer to pregnancy or pregnant persons.
You would have learned all about this if you had studied law. I’m sure they must have these concepts where you’re from.