Are you sure the IRS has finished processing the 2019 return?
When did you file it? Did you efile it?
So are you looking at your 2019 return to get the actual 2019 AGI?
FAQ: How do I find last year's AGI?
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947
Is your filing status single? If the 2019 return was married filing jointly, then for the 2020 efile each spouse uses the same total 2019 AGI; do not divide or allocate it.
Because of the ongoing pandemic since last winter, the IRS has not processed a lot of 2019 returns filed on paper, problem returns that are requiring more processing, or those who filed late in the year such as mid-November 2020 or later. Have you tried using an AGI of 0?