Just to echo what a few people have said here- I had the exact same scenario- 2020 efile rejected for 2019 AGI even after I verified my 2019 AGI with the IRS. It worked for me to put "0" in for AGI. I am filing jointly and entered "0" for 2019 AGI for both my spouse and myself. Once entering a "0" the return was accepted.
My taxes were filed relatively late for 2019 (maybe about October of 2020) and that appears to be a factor here.
