You say "So I attended university from 2016-2020. My parents claimed me on their taxes from 2016-2018. I claimed myself in 2019. All 4 of those years we used the American opportunity credit (AOC)."
That seems to say you claimed the AOC on your own return for 2019. Be aware that a full time unmarried student, under age 24, even if you don't qualify as a dependent, is only eligible for the refundable portion of the American Opportunity Credit if he supports himself by working. You cannot be supporting yourself on parental support, 529 plans or student loans & grants. You usually must have actually paid tuition, not had it paid by scholarships & grants. It is usually best if the parent claims that credit.
