Numbers app files not opening after upgrade to Monterey. (file name) "can't be opened right now"

Hello, after i upgraded to Monterey, some Numbers spreadsheets won't open. I get the error msg:

(file name) "can't be opened right now". Numbers couldn't read the file.

Now i understand that this is a corrupt file msg. I called apple and they are insisting that its a corrupt file, but that makes zero sense since i was able to open and work with these spreadsheets before the upgrade when i was on Mojave. And how can 30 different spreadsheets that all worked before the upgrade all be corrupt?

Has anyone else dealt with this issue? Thanks you!