A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Please back up just a bit :-) You clearly stated in your original message that your Excel version is 16.16.22 [which is Office 2016 for Mac] but you selected Office 2011 as the Office Product. That appears to have caused some confusion. Also, the version of macOS is not a problem... Your edition of Mac Office requires macOS 10.10.x or later, so that isn't the problem.
Are you able to create new workbook files? Are you able to save other workbook files or does this pertain to just this one particular workbook? If the latter, what is the source of the file? What additional details can you provide?
It sounds like the problem is exactly what the notification explains: The Office software has not been activated. The typical causes are:
- the user had a 30-Day free trial which has expired, or
- the one time purchase software actually hasn't been registered/activated, or
- the Office /Microsoft 365 subscription has lapsed.
How did you obtain Mac Office: By subscription or by one-time purchase? When did you purchase/subscribe? You can go to Excel> About Microsoft Excel in the main menu to verify the Version & determine the type of License for your Office software. Include those details in your reply.