If he checked off that he "could be (can be) claimed as a dependent of another" but already knows that you will not be claiming him, he should uncheck this box as this does not really apply to him. This is more for those who truly are not sure if someone else (parent, grandparent, etc.) that "can" claim them will actually be claiming them for a specific tax year. Again, since he knows you will not be claiming him, he should just uncheck that box and check the box that asks about the 50% or more. That will ensure the system accurately transmits the proper information to the IRS and then he will (provided all else allows him to) receive the 3rd stimulus payment. Make sure to tell him to provide the banking information that he wishes to use for both any refund due to him as well as to make sure that the stimulus payment goes to the bank and does not get mailed out. As it is looking right now, this could take many months to get to taxpayers.
