@LifeInAHamsterWheel don't take it too much to heart. It's only first year which is very much a settling in time IME. It's a huge change from primary, they're trying to adjust to that and make new friends, etc
Added to that it was a really hard year for them, all the extra rules and restrictions, masks, bubbles. It's very difficult for them no matter how blasé they might appear.
Celebrate the good marks, he can work on the other subjects next year. A family friend was the head of a well known secondary school until he retired. His philosophy is to really 'accentuate the positive', really praise them when they do well, it's great for their confidence and this helps with the subjects they find harder.
Don't be hard on yourself either, parenting teens is a minefield 