My 2020 AGI isn't on the IRS website, I filed my taxes last year (I have my forms and receipts at hand), is this an error on the IRS' side?

[DoninGA]

The IRS probably does not have your 2020 AGI in their database

Enter a 0 (zero) for the 2020 AGI and e-file the 2021 tax return again.

[T_Wheeler]

If the IRS has not processed your 2020 return yet, they may not yet have recorded the AGI. I read last year that if that happens, entering a 2020 AGI of $0 (for E-file purposes only) will allow the E-File to go through. I don't know first hand if that is true or not, but it shouldn't hurt to try. If not, you'll have to mail in your return.