Don’t worry too much about school. Your focus should be on the plan that your doctors recommend, and taking care of your health.
If that means surgery in December, that’s what you do.
My son had a big surgery in high school, and although it was in the summer, he wasn’t able to participate in most of his extracurriculars (including band) the following year. He also had an emergency hospitalization during school that year.
His teachers and the school nurse were all amazing throughout everything. It wasn’t hard for him to catch up. In his college app, he decided not to mention anything about his health except in the “additional information” section. He just wrote one sentence saying that health issues requiring surgery/hospitalization prevented him from doing his extracurriculars that year. It was all no big deal in the long run. Your situation might require more explanation, but your guidance counselor can do that on your behalf.
My niece has just missed more than half of her junior year due to a transplant and other issues. Her school and teachers have been amazing. I’m sure there are some schools/teachers that aren’t, but I think most of them are very sympathetic to students facing these sorts of things.
Junior year is a good time to do college visits, so you could try to squeeze some in before the surgery. Best of luck to you, and take care of yourself, above all. Whenever you do the surgery, you’ll get through it and hopefully be in a much better position to take on your upcoming studies in good health.