I just completed my 2020 taxes with turbo tax. The IRS wouldn't except my e-file so I changed the filing to mail-in now it say I have amended my 2020 taxes??

[Tahoe2]

I believe that the IRS won't accept your return because they haven't processed your 2019 return yet.  As a result they can't tie out to your AGI.   The IRS has indicated in a Jan update that to e-file your 2020 return you should simply change 2019 AGI indicated on TurboTax to zero.   For joint returns be sure to adjust both parties' AGI.

[Tahoe2]

This solution works and TurboTax should alert other users who are having their 2020 returns rejected. 

[fanfare]

AGI = zero works for some filers, but not always.