Since the WD My Cloud Home update which just occurred, Plex Media Server is no longer available under the “Do More” tab.
It is available under my main Login, however, when I sign into my My Cloud with the details of the Username that my Plex Folder is saved in, it is no longer available as an option to enable.
Have you opened a Support Case? If not opened, for more information, please contact the WD Technical Support team for the best assistance and troubleshooting:
Same here, PLEX is not listed in DO MORE page, and I just opened a support case to know how to solve this issue