Using the TurboTax personal edition software, a 2020 amended tax return can only be printed and mailed, it cannot be e-filed.
See this TurboTax support FAQ for amending a 2020 tax return originally completed and filed using TurboTax - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/00/27439
