i think sport, exspecially in schools, should always be mixed.

Girls' teams exist entirely to guarantee girls a number of slots, on the presumption that on average in most sports once you hit puberty generally the boys will start to dramatically outperform the girls due to things like size, upper body strength and other traits that are broadly connected to testosterone levels. Then you have things like chess, where you still have a women's league, but that basically exists because "not enough" women play chess and the notion is that a smaller talent pool broadly means easier competition that will in turn be more approachable.

Mixed teams in school sports as a general practice won't happen unless specific minimums are mandated, because it would impact competitiveness.

At the same time, under Title IX, if there is no girl's team and a girl wants to play a sport she must be allowed to try out and must be allowed to play if she can pass try outs. The reverse is not required under current interpretations, leading to a weirdly discriminatory interpretation of a law banning discrimination.