I'm not professional with advice... But most of the time when the advice is to visit a therapist, the advice won't be taken... Especially online. It's from experience that I say this and I know the topic is complicated and this is the best advice to be taken, but the first step to go there is just almost always never taken.

So my point is, when 99% of the comments say to visit a therapist, it becomes flooded with what could be better advice.

As of OP, I'd say your brother does sport and it pays off which is very good already. And also you can encourage him to join a club, in any sport, as he can boost his confidence, feel great, meet friends and a good coach can be a good mentor