How to improve self esteem in DS(12)?

[BonnesVacances]

DS used to be really friendly and outgoing, but over the last few years he's become more insular and lacking in confidence. He asked us a couple of years ago to help him improve his self esteem. I looked into this and he started going to Karate which he really loved, until he got to the sparring stage and he didn't like that, so quit.

So now he's started in Y7 and hasn't really made any friends and so hates going to school. He's not sporty, more of an academic tbh, so we struggle to find things that he can do outside of school. He loves acting and goes to a drama club once a week, but he doesn't want to join any other groups.

What can you suggest that will improve his interaction with other boys and help him to open up and be friendlier? Especially for a non-sporty lad?