So I’m looking for a good coming of age story with a child that feels themself as smart and capable as any adult fighting for agency over their own life despite being seen as a minor or too young by everyone else.

I'm very much a fan of fanfiction and stories that have a similar vibe. I also generally see this in fanfiction where the main character is a child who was reborn with memories intact from a previous life and has issues with authority and a past/ knowledge of the character/ story they got reborn into that makes them feel like letting parents, the government, or just adults in general be in charge of their life is a bad idea. I'm not sure I've seen any normal published books like that though. I would love to see one where the MC is just a child prodigy or something and is making the same struggles without it being fanfiction or reincarnation. I guess the closest I could think of is Ender's Game but that isn't quite right and it is more of adults expecting too much from a child and using him as a sacrifice for the greater good.