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://protect-au.mimecast.com/s/WhwpCjZrzQuYZAyiWWXRI?domain=excelforum.com

https://protect-au.mimecast.com/s/qMVuCk8vAQhko4qCVr9J6?domain=answers.microsoft.com