Excel locking formatting uninvited

I am using Excel for Mac 2016 on a MacBook Air running Ventura 13.1. I have had a couple of instances where all the formatting has locked as though the sheet / workbook was protected. The only icon that works is Cell Style. When I look in the Review tab, the options are to Protect Sheet and Protect Workbook, so the sheet is "unprotected". I dont know what I have done and how to undo it. Any ideas?

Thanks

Evan