The IRS may very well not have the 2019 AGI associated with your name and Social Security number in their database. The IRS has been very slow to process 2019 tax return so if the 2019 return has not been processed or it completed processing in late 2020 or early 2021, the 2019 AGI will not be available to the IRS.
Entering a 0 (zero) for the 2019 AGI is not lying you are using the best available AGI to get the 2020 tax return e-filed. If the 0 for the 2019 AGI is also rejected by the IRS then your only other option is to print and mail the 2020 tax return.
See this TurboTax support FAQ for how to print a tax return for mailing - https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...
