The TurboTax online editions are only for tax year 2021. You Cannot combine tax year 2020 and 2021 on a tax year 2021 tax return. Each tax year is completed and filed separately.
To complete and file a 2020 tax return using TurboTax you would need to purchase, download and install on a personal computer one of the 2020 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
A 2020 tax return can only be printed and mailed, it cannot be e-filed.
