The hardest part with this conversation is that there isn't really a satisfying short answer, but I can try to give one.
The biological differences between men and women that most people think of as giving men an advantage over women in sports are counteracted by hormone replacement therapy, and do not give trans women athletes an advantage over cis women athletes. Some of the arguments, such as bone density being higher in men, are literally taken word-for-word out of segregationist rhetoric- and ignores the fact that black women have higher bone density than most men. There is not a clear scientific reason to exclude trans women who are undergoing HRT from sports.
That's it, that's the answer. But I feel like that's just asking you to take my word for it- all of that and more is backed up by science in the report I linked.
I agree that this seems to be the intent behind Lemmy. But, I also think that, right now, there is such a big influx of people that need accounts that we need to route them into as many instances as possible to keep server stress down. And that means that a lot of communities will be generalized by the new users.
I agree with other comment that this will likely happen organically over time. After things stabilize I think we'll see communities begin to merge with identical or similar communities on other instances. And at that point server admins can start to take a bit more of a firm hand with their instances to try and do exactly what you're describing, if that's what they really wanted.