You, most likely, qualify for the AOTC for 2021.
There are two 4 year rules. The first one says you must not have completed four academic years before 1-1-21, Graduating in May 2021 means you met that rule. Note that if you had started grad school in the fall of 21, your grad school tuition would also qualify for the AOTC (because you had not completed 4 years of college by the beginning of the tax year).
The 2nd rule is that you (and/or your parents) may not claim the AOTC more than 4 times on your education. Since 4 academic years of college usually takes 5 calendar/tax years, it's possible that you don't meet this rule. So, if you (or you parents) had claimed the AOTC in 2017, 2018, 2019 and 2020, you would not be allowed it for 2021.
