Welcome to the forum.
In this case, the attachment really porovides us with no clues.
How EXACTLY is each of you accessing the file? Via a browser? Via the desktop? When you say OneDrive, do you in fact mean SharePoint? Is this over a network?
It is these details that will be relevant, not the contents of the workbook, unless you are saying that you are able to co-author other workbooks, but not this one.
More details, please!
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