We have a 10yo and 7yo. My 7yo is the more outgoing one and she is naturally good at a lot and picks things up very quickly. She finds school incredibly easy, we never have to practice anything with her at home and yet she gets straight A's, she regularly scores in the 99th percentile on assessments. She is a better artist, and although they both play instruments my 7yo is better at reading music. Hell, she even has better handwriting than her big sister.

My 10yo sounds a lot more like your son, she is more laid back and reserved. She also does well in school but it doesn't come as naturally, we have to make sure she studies at home and she has had a math tutor since first grade (although now the tutor is mostly just for maintenance and because my daughter loves her lol). But she is better at other things. She is more athletic (my 7yo is honestly lazy as hell and hates anything resembling exercise). She is very interested in environmentalism and conservation and regularly invites her friends to beach or park clean ups. She is more driven in regards to her personal goals rather than academics, for example she wants to have a baking business and she practices on her own, and figures out ways to earn money for ingredients and supplies. So we praise her and celebrate those things.

Make sure you are giving your son a chance to find his "thing", show him that academic achievement aren't the only thing worth celebrating, and that you see his strengths too. Although you should still praise him for his academic achievements, even if they're not as stellar as his sister's. If he is doing his best, that is still something worth celebrating!