I'm looking for something authoritative (even a mention on the IRS website) that says that an EIP2 that was paid in 2021 needs to be accounted for on the 2020 tax return.
Perhaps it would help to review what is really happening:
The funds were paid out as Advanced payment against a projection. The projection used 2018 or 2019 tax returns. But 2020 is the Actuals. You use the 2020 return to reconcile what a person is entitled to, against what they got.
You might want to bookmark these links and read the IRS guidance.
Interactive wizards portal for determining dependency:
