I am having similar problems e-filing amended returns and I'm not arguing at all I just don't understand because in the instructions it specifically tells you save as under another file name but work off the original.

https://proconnect.intuit.com/community/amend-tax-return/help/how-do-i-amend-an-individual-return-us...

I understand this is 2020 but I do not see anything for 2021.