Yes you can e-file your 2021 return. You will be asked for your 2020 AGI from line 11 of your 2020 Form 1040 in order to e-file. If you filed late or your 2020 AGI did not make it into the backlogged IRS system you can try using zero as your 2020 AGI.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**