Applying as a Repeat Junior?

I’m a current junior at a private school that’s not meeting my needs. I’m thinking of applying to a prep school (Groton, Andover, or CA) to repeat my 11th grade year. I’m just worried about how this will look on college applications. I’m worried about how a repeat year will look - I don’t want to be a one year senior and I think I might need that year for my academics. This would be my third high school and I don’t know how that would look. My freshman year school focused on grades rather than learning and my sophomore year school (and current school) has a great arts program but no academic rigor. I want somewhere that I can focus on theater and also push myself academically. Is there any point applying this late? And will going to three high schools hurt me when applying to college?
Thanks for any help - I know this is a tad incoherent but I’m having some trouble figuring out my thoughts on this.

Also : would it be worth it applying to any of these schools as a senior? I know that CA rarely accepts one year seniors. Does anyone have experience with that?

Repeating a year is very common for new students to boarding schools; College admissions will not bat an eye

Some schools do not accept new seniors. Those schools that do accept new seniors are often using those spaces for athletic recruits. For the college admissions process, you will be at a huge disadvantage as a new senior vs a repeat junior.