It does not matter that your parents received the 3rd stimulus payment for you when you were their dependent is based on their 2020 tax return.
The Recovery Rebate Credit for you in the amount of $1,400 is based on your 2021 tax return where you are not a dependent.
It is perfectly legal for your parents to receive the stimulus payment for you in one year and you to receive the payment in another year, that is a loophole in the tax code.
