can't add a new sheet after sheet has been protected then unprotected

I’m using LibreOffice version After I protected my spreadsheet, I can no longer add a spreadsheet, even if I un-protect it again. The plus sign is visible to add a sheet but has no affect. Additionally, I can’t insert or delete a column or row in protected mode even if the boxes are checked to do so.

Uncheck menu item Tools/Protect Spreadsheet Structure

Yes, Thank you. Now I can add and delete new sheets. But still in protected mode I still can’t rename the original sheet or delete rows and columns. Do you have any suggestions?

Yes, the protected sheet cannot be renamed.
With regard to deleting columns (rows), then (with checked boxes) it is possible only if all cells in the column (row) are not protected.