Question about WD My Book Duo

I would copy all data to another hard drive, then reformat the WD Mybook. Then copy some unimportant files to the disk and try to delete them.

If it works, great, otherwise the hard drive is probably damaged.

NTFS (Windows NT file system) on MacOS is read-only. However, there are filesystem drivers under MacOS that must be installed separately. Otherwise reformat to FATxx (reformatting = data loss because a new empty file system is created).