Here's what worked for me: enter 0 in the AGI box, rather than any actual dollar amount. I didn't think this up by myself, others here have suggested it, but it worked for me when nothing else did.
My situation: my spouse died in 2019, and I ran into the same problem with my 2019 return last year that everyone else here has had. TurboTax had no solution so I filed a paper return. Then this year my 2020 return was rejected for "incorrect AGI" even though the value was indisputably correct.
But putting 0 into the AGI box rather than the correct value worked. My federal return was accepted yesterday, which allowed my Colorado state return to also be accepted. I can only guess at why it worked; apparently if the IRS sees a zero in that field it gives you a fresh start. Or something.
Now then: Why the heck TurboTax does not provide this advice is a complete mystery, and not helpful.
Good luck!
