I’m not sure HS was ever fun so I personally would not make that my goal. Instead, I would talk over goals with the kid. As I said, I have always thought that the goal was to help the kid have a happy, productive, fulfilling adult life. I then try to work backwards with them over proximate goals and how best to meet them. But the OP and his son can think about the goals they think are most appropriate.
A friend of mine is a foreign-born CEO of a pretty big company. He asked me to talk with his very bright son who was only interested in math/computers and didn’t understand why he should try to do well in some of the other courses. Despite remarkable success, my friend and his wife don’t have any credibility with the son because neither had experience with the US educational system. So, I spent a couple of hours with him working backwards from longer-term goals and explained the game of getting into a college. We talked about the benefits that come from playing the sorting game and how to minimize the costs. I left the choices up to him. His father tells me that the son is now applying himself very diligently following the strategy I suggested and the father is very pleased.
A lot of this comes down to the specific student: what does he like, what is she especially good at, what is she especially bad at, any diagnosed issues, how mature, any real goals yet, what can the school offer, are there financial constraints, is homeschooling an option, what has already worked or failed, et cetera, ad infinitum. Meet the kid where he is, see where he wants to go, make sure he’s as functional as possible in his weak areas, make sure he has room to grow in his strengths.
OP, I’d let him walk through HS, but explain that by doing so he’s making a lot of other choices at the same time. Make him map out a full path from this year through college and grad school. What classes, what major, what schools, and then point out the gaps where the plan won’t work. Top schools don’t need to settle for kids that could do better whenever they want to, they choose the kids that have shown what they can do. (And if he thinks high school is boring and not worth the effort just wait until he’s paying $60k to scoff at the same math classes he won’t take now. )
I think there’s a happy medium here. Kids don’t always know what’s in their best interests and you don’t want to close doors, but @thumper1 often writes that her kid was able to go into engineering without taking Calculus in high school, and I can tell you that my older son got into Harvard (and my younger son into U. of Chicago) without taking AP English. They both had taken lots of other APs and they each got an A+ in the English elective they took instead. (They also both got rejected from other equally selective colleges where that missing AP may have made a difference.) They were both avid readers and did very well on the verbal portion of the SAT, but they were so much happier senior year not having to read a pile of stuffy classics.
At any rate it sounds like the OP’s kid is listening to teachers and I agree that helping him perform better with organizational skills may be more effective for him.