I think we may be talking at cross purposes. My understanding of transgenderism is that - leaving aside intersex people and people with any one of a handful of extremely rare chromosomal conditions - male and female sexes are fixed biological categories. Gender, on the other hand, is fluid. So, male and female is fixed, but girl/woman and boy/man are not.
This means you can have a girl (gender) in a male (sex) body, going through male (sex) puberty and having their development guided by male (sex) hormones like testosterone, but this doesn’t invalidate her identity (gender) as a girl/woman, because gender identity is distinct from sex and is amenable to change.
That’s my understanding, at any rate. I’m far from an expert on this.
Now, it’s well known that the average teenage male has much more testosterone in his system than the average teenage female. Indeed, the average teenage male has much more testosterone in his system than a teenage female with higher than average testosterone. In your previous post, you said: “Some of these hormones are different on average in boys and girls”, but the word ‘different’ is doing quite a lot of work. According to this source ( Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance ) the average teenage male produces thirty times as much testosterone as females of any age. While the levels of some sex hormones are different on average in males and females, the difference, on average, is vast and insurmountable.
Now, I acknowledge your point that trans experiences were excluded from the studies from which these averages were derived, but if gender is distinct from biological sex, then there’s no reason to believe their inclusion would’ve influenced the results in either direction. To the best of my knowledge, there’s no evidence that - prior to treatment - the testosterone levels of a typical transgender girl are different to those of a typical cisgender boy.
Therefore, if a transgender girl is allowed to compete against cisgender girls then, all other things being equal, she would expect to win because of the higher amount of male sex hormones to which she was exposed during puberty. That’s why I don’t feel it’s fair to allow transgender girls to compete with cisgender girls.
In this example, the Norwegian girls would have an advantage, but it’s not the same type of advantage that transgender teenage girls have over cisgender teenage girls. To further the analogy, if the sport were basketball, and Norwegian girls were, on average, fourteen feet tall, then I’d imagine they would be excluded. There’d be no point competing against them.
I agree that these sports should certainly get more support than they currently do. However, the number of sports in which girls have an advantage is very small, and it excludes virtually all the most popular school sports (football, basketball, short and middle-distance running, all jumping and throwing events, nearly all gymnastic events, soccer, tennis, swimming, and many others). These sports are the ones which most people, including most transgender people, enjoy participating in. For this reason, I don’t think supporting the more niche activities in which women perform better would actually do anything to solve the main issue.