According to this article dated 7 days ago you might be able to efile. But you need to use the Desktop program and it has to know if your original 2020 return was efiled and Accepted. So before you amend you have to update the program with your efile status. Open your return and go up to the top black menu bar first item
File > Electronic Filing > Check Electronic Filing Status
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/e-file-1040x-amend-return/L9t...
