If he is eligible for a stimulus payment based on his 2020 tax return, he will get the payment as a credit on his 2020 tax return. It will not be a separate check or payment. It will be a credit on his tax return. The amount will depend on his income. If he cannot be claimed as a dependent and his 2020 income is $75,000 or less he will get a $1,200 credit on his tax return. The credit will be applied towards any tax that he owes for 2020, so he will not necessarily get a $1,200 tax refund.
Note that one of the eligibility requirements is that no one CAN claim him as a dependent. It doesn't matter whether you or someone else actually claims him or not. What matters is whether anyone could claim him as a dependent. If he could be claimed as a dependent, he is not eligible for the stimulus credit.
He must also be a U.S. citizen or resident alien and have a Social Security number that is valid for work.
