If he is eligible to be claimed as a dependent, he must check the box that says he can be claimed, even if the person who could claim him doesn't want to. For 2020, he can be claimed
a) if he earned less than $4250 of taxable income and filed no tax return, or only filed a return to claim a refund of withholding and claimed no other credits;
b) you paid more than half his support.
If he files a 2020 return and can't be claimed as a credit, the first $1200 payment will be included in his refund. Possibly also the second payment, if President Trump eventually signs a bill.
