See this TurboTax FAQ on how to find your AGI
https://ttlc.intuit.com/replies/3301618
You can get free 2019 tax transcript from the IRS
https://www.irs.gov/individuals/get-transcript
If you filed late last year there is a good chance that the 2019 AGI never was entered into the e-file database. Try using 0 (zero) for the AGI.
If you filed an amended return use the AGI on the first filed tax return.
If it continues to reject then the AGI in the IRS database might be in error. Mail filing is the only option.
Also see: https://www.taxpolicycenter.org/taxvox/are-irs-security-tools-blocking-millions-people-filing-electronically
https://www.forbes.com/sites/howardgleckman/2021/04/26/are-irs-security-tools-blocking-millions-of-people-from-filing-electronically/?sh=529e1d891a76
Sometimes the database gets set back to zero. Try again with zero AGI. You can also lie to TurboTax and say that you did not file taxes last year and it will go through without AGI. Lying to TurboTax is not the same as lying to the IRS.