I am having the same issue. I have two company files, 1) One of these files I 'upgraded' when told "

The company file "XXX.qb2020" was saved with a previous version of QuickBooks. To open this company file with QuickBooks 2020 Desktop Mac, it must be upgraded." This file now gives me the error, "The document “XXX.qb2020” could not be opened. The file isn’t in the correct format. The file might be corrupted, truncated, or in an unexpected format."

2) My second company file requires an update in order to be opened (I'm hesitant to do that, because that's the process I followed to get to this error.)

I saw your workaround for invoicing, but is there a workaround for those of us with these company files and the latest  update already installed, "QuickBooks 19.1.14.1102 R15.1 is currently the newest version available."

Thank you.