Unable to save changes to documents to numbers
on my iMac I updated to Big Sur on 11/12/20 & also updated to the latest version on Numbers-Each time I try to save changes to my current documents on numbers, I get a message saying document is damaged & can't be opened-Message offers 3 solutions: Duplicate, Discard, & Cancel-none of which helps.,Does anyone have a solution for this problem? Thanks
iMac 21.5″, macOS 11.0