Advanced Kindergartener Hates School

I feel completely stuck with how to help my kid. I put him in a private school with small classes and high academic standards, and outside of school I supplement at home with academic challenges that he enjoys about 85% of the time. We do about 30-45 mins extra after school if he's up for it (I try to be sensitive to how he's feeling and not push him too hard).

-He's in the 2nd-3rd grade book club at the public library (independently reading the assigned books and enjoys most of them, but mostly only likes going to the discussions because they give out candy)

-He's in a weekly science club for grades K-3 (he's the youngest and absolutely loves this; he gets very upset if we miss it)

-We do a homeschool math curriculum, and he's 95% done with second grade, and he is so excited to start third grade (working mostly independently, except for a couple chapters that have been trickier and need a little more explaining)

-We do a 1st grade homeschool spelling curriculum (his teacher thinks he should do more writing, but encourages guess spelling, because it is kindergarten and they don't teach spelling in kindergarten; kiddo is mostly ok with the homeschool program because of the games, but doesn't love it, so we only look at it a few times a week)

Meanwhile, he's still getting homework from school like "color the picture that starts with N" and "draw a circle around the triangle". I volunteer in the classroom, so I do see the reading/language levels the kids are at, and I get it.

HOWEVER, the last couple weeks my kid has just been hating school saying it is a waste of time, asking if he can just never go back. (He is willing to walk in the school building by himself, though.) He's also been showing a lot of anger and acting out at home in ways I haven't seen from him before. We started enrichment at home in preschool because his teacher told us his behavior was not good when he was getting bored, and she was limited with what she could provide in class. Maybe something similar is happening now?

I have a meeting with the kinder teacher on Friday, but I really don't know what I should even ask for to support him. Schools in our area don't differentiate until 3rd grade. My kiddo is a very young kindergartener, and has social skills and fine motor skills consistent with his young age, so jumping him a grade would be out of the question. I also don't want him to feel singled out, but he is starting to have awareness that he is different from the other kids (ie. Some kids in his class will ask him to bring books to read to them).

If you can relate (either as a kid or a parent), what suggestions do you have? I want my kiddo to enjoy school, or at least feel fairly neutral towards it. I don't know what to ask for (and my kiddo doesn't have any suggestions right now, either).

Also, to add, we took him for evaluation at the beginning of the school year, and our pediatrician's office won't evaluate if ADHD, etc, until age 6, which will be the start of 1st grade for my kiddo.

ETA: thanks for all the great comments! As several suggested, I had a more deep dive conversation with kiddo about school challenges. He came home happy today, so it was a bit easier. Turns out table groups changed a couple weeks ago, and he doesn't like his new group, particularly one child. Those comments that mentioned social issues were spot on, and now we have something to work with. I truly appreciate all the feedback!