There is some merit to the idea in some highly competitive sports that trans women may retain some biological advantage over cis women.

However, the "protect women's sports" crowd isn't interested in having a good faith discussion about it. For starters, they'll cry against even the idea of preteen trans girls playing with cis girls. Or against trans women in a social women's sport club. Outside of elite sports, the argument is literally completely irrelevant because so many other factors are far, far more significant. When you have a league consisting of people who have been playing casually for a year or two in addition to people who were only a few spots away from going pro, the difference between the genders is an irrelevancy.

But there have also been studies that say the biological advantage is overstated. One study showed that 2 years after starting HRT, trans women retained none of the advantage they started with in push ups or sit ups, and that the advantage in a middle distance run halved. The study didn't say, but I'd hypothesise that after 5 years that, too, would be gone.

So at the elite levels, it's fair to say that each sport should be making its own decision based on the types of fitness and skills involved. And those decisions should be based on the weight of evidence, not—as is usually the case today—on the vibes or because of political lobbying. Some restrictions, especially pre-hormonal transition and shortly after, are likely warranted in many cases. Longer-term restrictions are less defensible.

And all of this assumes someone who went through a normal male puberty. It says nothing of the fact that the same crowd arguing against trans people in sport are the ones arguing against puberty blockers and allowing children to make decisions for themselves with the aid of their parents and doctors, without government intervening. If that were allowed, many of those biological advantages never would have been able to develop in the first place.