For many (myself included) the AGI shown on the 2020 tax return is wrong. That's because of the change in 2020 tax law where the IRS exempted the first $10K of unemployment from being taxed. They passed that law retroactively after I had already filed and received my refund. So I didn't get my additional refund until months later. That effectively changed my AGI, though I don't think it should have. (Income is income, taxed or not).
What I had to do after making a backup of my originally filed 2020 tax return, was go into TTX 2020 to change it. Turns out, I didn't need to because an update issued by TurboTax basically changed it for me, without my knowledge or consent.
I ended up pulling a transcript of my 2020 tax return at www.irs.gov/individual/get-transcript. Turns out, the AGIN on the transcript is different from the one in TurboTax, even after a program update supposedly "corrected" it. So when it's time I'll be using the AGI on the Transcript.
