会 usually means "can/could/be able to"，but it means "be good at"in this sentence. "He is not only good at studying but also playing."

be good at

“can” or “be able to”

Thanks so much

会 means 'able to do'.This sentence want to emphasize：He is not a bookworm who only knows how to study, nor a boy who is fond of playing. He has a good way to do both of these things well. Therefore, 会 means 'do well in'