A 2019 tax return filed in December of 2020 could only have been completed and filed using the TurboTax desktop editions for tax year 2019.
The TurboTax online edition are Only for tax year 2020 and you could not have e-filed a tax return in December of 2020 since e-filing was not available for the 2020 tax year until January 6, 2021.
To complete and file a 2019 tax return using TurboTax you would need to purchase, download and install on a personal computer one of the 2019 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
A 2019 tax return can only be printed and mailed, it cannot be e-filed.
