Looks like your viewing the My Cloud through the MyCloud.com web portal interface. Don’t recall being able to shut down the My Cloud via the MyCloud.com web portal (or the older WD2Go.com web portal) or when using the WD My Cloud mobile apps.
Apparently the v2.x firmware My Cloud’s are missing the Shutdown option within the My Cloud Dashboard (or were in previous v2.x firmware versions).
Typically one can shut down the My Cloud on the local network by clicking on the Shutdown button (for v4.x firmware versions) from within the My Cloud Dashboard. One can also shut down the My Cloud using the WD Access software. It is also possible to issue the shutdown command (again for v4.x firmware versions) using SSH.
There is more discussion on shutting down the My Cloud in the following threads:
https://community.wd.com/t/safe-shutdown/147307
https://community.wd.com/t/shutdown-mycloud-from-mobile/157418
https://community.wd.com/t/how-to-safely-shutdown-mycloud/155265
