It does fit the scenario, it does not matter if your return was mailed or e-filed in 2020. The IRS was backlogged processing 2020 returns, which again TurboTax has no idea of when your return was processed by the IRS. TurboTax or any other tax software would have no idea when your return was processed, so the program would not know to tell you to add a zero.
TurboTax can only ask how you filed in the prior year in order to enter the AGI. They still would not know you need to enter a zero because your return was processed late.
