1.) No at least part of at least 3 months.
2.) It would disqualify him as your "Qualifying Child" dependent, however he could be your "Qualifying Relative" dependent.
3,) No, not as your dependent, the payment/credit would be based on your income.
Yes if he files as non-dependent he would get the payment as a credit.
Since he was not under 24 at the end of 2021, he would not be claimed as your Qualifying Child.
To be your qualifying relative, he would have had 4,300 or less Gross Income and you would have needed to have supplied more than half his support.
If he did not live at your home after graduation, that would also eliminate his as your dependent.
More information about dependent requirements
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