As Quickbooks is functional I'm a bit surprised that a 'repair' might be the solution but I did it anyway, as instructed. This has not solved the problem.

I mentioned earlier that File Doctor did not help either. it simply crashed. Same result after the repair.

I've worked my way chronologically backward through all my backups. All are bad except, perhaps, the very oldest from Feb 20. If that is no good I'll have to go to my end of year backup and then re-enter almost three months of work. That is a LOT of work. This is beyond  depressing. I would have thought that Quickbooks would have better data integrity testing built in to it so you could never get into a situation like this where it's gone undetected for so long.