Forum Discussion
Excel version 16.34 has not fixed this issue
excel-prompts-you-to-grant-access-to-files-and-then-hangs-or-shows-a-warning-that-it-cannot-open-the-xlsx-file-because-the-format-or-extension-is-not-valid I'm using Mac OS 14.7.2 and Office 365, Ex...
A couple things to check:
Verify your startup volume:
How to repair a Mac disk with Disk Utility -
Are you saving locally or to a network or internet location?