My kids aren't as dumb as I make them seem. Middle kid typically could figure out Algebra before it was taught to her (teacher would let them try before she taught something, and middle kid could figure it out with no instruction). Same for when she was forced to take a Chemistry final without taking the HS Chem course and wasn't allowed to borrow the HS Chem textbook - she figured out how to do the pH problems just by taking the logical route and applying what she did know. But I don't think that makes her gifted or anything special, just rational and logical. We have never tried to accelerate her and she wouldn't go teach herself math on her own...she probably would watch Netflix.
There have been a few odd reactions to her. One kid wouldn't go out with my eldest because his younger brother said middle kid was scary (not in looks, in intelligence). And some kids kind of avoid her because of stuff she likes to discuss, though she certainly has friends that are like her.
I deal with enough politics and drama in sports. I have had to deal with some school politics (including that Chem final), but I try to avoid it. She is bored out of her mind in HS, but I think that will change once she gets to college - I have seen it change for the PG kids I know (who went where there were others like them). Only two more years - she can just concentrate on improving the athletic skills for her two sports.
And as for the OP's original question - delving more deeply into other subjects - unfortunately there is only so far you can go in certain subjects in US high schools. Maybe the kiddo can take a few foreign languages, since they might not have the chance to do that if they go into a STEM college degree program. Or take additional history courses. My older two always have/did take six core courses - one more than normal - to keep themselves busy.
