Corrupt file error on an often used .XLSX document on my iMac. Using Office 365

I have a very important file that is giving me the following error when trying to open it using Microsoft Office 365.

"Excel cannot open the file 'Customer Info.xlsx' because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file."

With several hours of research, I have not been able to find a solution to be able to view the file. This file has been in use (and rarely every modified) for well over a year and has never had issues.

Steps taken:

• Tried changing the extension to .xls and .txt
• Tried to open in Numbers app
• Tried to open in Microsoft office 360 online
• There is no option to open and repair in Office 365
• I used the disk utility on my iMac to see if there were any errors... it was clean
• I downloaded a 3rd party app to try to open it "LibreOffice" from online discussion boards about the issue.

I am operating with Office v.16.62 and my Mac is Monterey v.12.3.1

What else can I do? There is very sensitive information in this file that I need access to ASAP.

Thank you.