Do colleges care if you repeat a year of high school?
Title. basically. I want to repeat my Junior year in an effort to improve my GPA more. Is this ok?
Colleges are perfectly indifferent to students either repeating a year or taking a gap year to enter a PG program prior to applying.
In affluent predominantly East Cost families, if a student is not "making the grades" or not "Ivy ready", it's commonplace for them to take a PG PostGraduate year at boarding school after high school in order to strengthen those academics. Another benefit is that if a said sibling is also an athlete, it gives them an extra season or two of playtime to improve their skills with the intent of getting recruited as an athlete. PG students typically are accepted more because they have a slight maturity advantage and voluntarily decided to spend more time preparing prior to applying to college so they can show evidence of their determination and hard work.
You do not have to go to a $65,000 a year boarding school to get most of the same benefits. You can as you say repeat your 11th grade or alternatively take college or dual enrollment courses this summer and the summer after high school and apply in the Fall either to a college with Mid-year matriculation or to a college with Rolling Admissions (meaning you can apply first come, first serve basis). There are many good colleges where you can be admitted Mid-year like Boston University, USC, or Cornell University if you choose to do so. In many cases, if they have no room for Fall Admissions, many elite colleges agree to accept the student with a delayed start.
The last thing I wanted to leave as an option is that you can also matriculate into your community college after HS, and earn As in as many core college courses as you can handle. From CC, you can transfer after 1 year or 2 years depending on how you do. I think if you had a 4.0 average and had 30-32 college credits in CC, you could transfer to many top universities. The upside with being a transfer student is that HS GPA and transcript won't matter as much or not as all.
Taking your time to show colleges your potential and best version of yourself is never a bad idea. I think too many college applicants are ill-prepared for college and find themselves in a precarious time crunch to 1.) Keep their As, 2.) Research Colleges, 3.) Take STD tests and prep classes, 4.) Work on essays, 5.) Have a financial aid roadmap etc. So this is a systemic problem with public education. This is not so much a problem with Private HSs or boarding schools.
Hope that is helpful to you.