[DNSB]

I would agree that you are likely running into Controlled Folder Access. Instead of creating your destination folder in your Documents folder, create it in the root of your user folder (c:\users\yourname\calibre) and then restore your library to that folder.

You may have to then tell calibre to use the existing library/libraries in the folder. I haven't restored a calibre library from export/import in quite a while. It was faster to do my changed file sync to backup rather than backing up the entire calibre library each time I wanted a backup.

Much easier than mucking around in Windows Defender to un-protect your files/folders.