When opening InDesign 2020 files I get a message that the file is damaged. See screenshot. The same file will open with Adobe 2019.
When opening the file in ID 2019, I get the message that links are missing. Perhaps ID 20 thinks that the file is damaged because the links are missing, so I get the damaged message.
Using InDesign 2020 on a late 2015 iMac running MacOS 10.14.6, 32GB Ram
Barry Cohen commented
Just now, a doc I created with ID 2020 a couple of days ago, and has opened fine every time has just given me the "Damage File" warning.