To complete and file a 2021or 2020 tax return using TurboTax you would need to purchase, download and install on a personal computer one of the desktop editions for each tax year required from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
A 2021 and 2020 tax return can only be printed and mailed, they cannot be e-filed using TurboTax.
When mailing tax return for multiple years you must use a separate envelope for each tax year.
NOTE - for a tax year 2020 return with a tax refund, the tax return must be mailed on or before April 15, 2024 or the tax refund will not be paid.
