Maybe it thinks you didn't file the original 2020 return? Did you efile it? I don't know if this will work for prior year returns and on Mac but for Windows you need to go up to to menu item
File > Electronic Filing > Check Electronic Filing Status
Then save your return with the status. Go to File-Save.
Or go into your original return and go though the FILE tab and say you want to mail it. Then you might need to print it out so it thinks you did.
