“Brave”

Someone needs to call their parents and explain your concern over their recent fatigue and persistent cough. Doesn't matter of it's fake.

Why would you tell a female to act more male? If that's the attitude in your school - that the best people are ones that act like men - then no wonder people consider this child brave for going against that

A child with possible dysphoria (or whatever is going on for them to make them feel this is the way they need to go) visibly responding to that in a way which makes them happier but is going to make them stand out a LOT amongst their peers is quite brave, is it not? Even if you don't agree that what they're doing is 'genuine' or you think it's 'annoying'.

I do think a boy doing GNC things is brave and a man as well.

Loads of men and boys are highly invested in perpetuating a very fixed view of what a man is. And can and are awful to non conforming males. Homophobic violence etc.

The other behaviour is bizarre and needs looking into.

Oh and the best way to reduce discrimination is to see the thing as normal not as something special etc. Also it might make other boys who want to wear a skirt less likely as they worry they're not brave enough.

Why would a boy who wants to be a girl be happy to continue in an all boy school?
The tiredness & cough should be reported for clinical advice.

If the student appears tired after exertion , even if it turns out to be mere affectation I would be informing the parents of this so they can take the child to the doctor's, especially if they have a persistent cough.
As to the student's bravery, well I suppose wearing a skirt in an all boy's school can't be easy but it is nice to think that the boys in this school are open to accept non gender conforming male pupils.
I don't really understand why you would say "If they were female we’d be telling them to buck up and be more male." If they are being told this by other students then those students should be reprimanded, if it is by teachers then that is appalling.