Cannot un-protect workbook structure (also can not freeze pains or new window)

Cannot un-protect workbook structure (also can not freeze pains or new window)

I have searched online and in these forums (save as a different file type, ungroup tabs, format all sells to not protected)

No joy...

This is an old workbook created on an older version of Excel, however I have a few others of the same pedigree which don't have this problem...

If I copy the worksheet to a new work book I can freeze.. however I have links to many other worksheets including SQL queries so this is not a solution.

I found below threads - unsolved.

https://www.excelforum.com/excel-general/1139125-freeze-panes-greyed-out.html

https://answers.microsoft.com/en-us/office/forum/office_2013_release-excel/excel-info-page-shows-protected-workbook-but-it/e8cf6c02-b23c-4ccc-a672-e3c4bc33e9f5