I've been having the same problem ever since the latest update that it wanted me to install the other day. (QB Mac 2020 v19.1.14 R15.1).

File says corrupt, so I pull an old file off of my backup server - it will open the backup file ONCE and then when I close, it is corrupt again...so now I have to go through this process just to view my information, and I can't make any changes because it goes corrupt every time.

Same problem on the laptop.  I think this update broke the software somehow... this is VERY frustrating.