Interesting viewing that is, it gets philosophical with regards fairness, which is the entire problem with this debate... it's ultimately philosophical. We can apply all the science in the world, but we can't truly define "fair" because it's not an objective concept. We can perhaps agree that fairness is equality in opportunity, but that's undefinable itself, it's again philosophical and not scientific. What does it mean? "Fairness" usually happens at someone's expense.
What this comes down to for me is the impact this has on opportunity for natural females. Sabine talks about how some ciswomen are born with higher natural levels of testosterone than even some men. These women already have an advantage over petite women. If we also allow high-testosterone transwomen to compete with ciswomen, the petite women are even more likely to be outcompeted. Ultimately it removes incentive for petite girls to even bother taking sport seriously as children. So while we create opportunity for transwomen, we remove opportunity for petite ciswomen. This is what I mean what I say "fairness" usually happens at someone else's expense. You can't be fair to everyone, which of course makes a complete mockery out of the concept of fairness.
This debate is more philosophical than scientific for this reason. We're talking about fairness first and foremost.