If one does a forum search (magnifying glass icon upper right) they’d see this issue (remote backup of a computer to a My Cloud) has been discussed in numerous threads.
Short answer is that neither Smartware nor Apple Time Machine will backup to a remote My Cloud. Officially the only way to access a My Cloud remotely is via FTP which is NOT secure, or via the WD My Cloud Desktop program, or via the WD My Cloud mobile apps for iOS or Android, or via the MyCloud.com web portal. WD removed the ability to remote map a drive through the WD2Go.com web portal last year when they released to OS3 firmware.
The unofficial solution for remote mapping a My Cloud is to install, via SSH, the CloudDAVMod which is discussed in the following link:
https://community.wd.com/t/app-clouddavmod-v1-0-for-firmware-v4-05-2016/161543
There are other unofficial methods of remote access but they too typically involve modifying or configuring the My Cloud OS via SSH. One potential option is to use WD Sync which will sync files to a My Cloud, both locally and remotely. Its not a good backup solution but is a way to have an off site collection of files (or folders) on a remote My Cloud. Another option is to use a third party backup/mirroring program, like Free File Sync (http://www.freefilesync.org/), that supports SFTP/FTPS and configure the My Cloud, via SSH, for SFTP/FTPS. Do a forum search as SFTP/FTPS has been discussed in other threads here.
Here are just a few prior threads, there are others, discussing remote computer backup:
https://community.wd.com/t/make-computer-folder-backup-to-a-remote-my-cloud/166490
https://community.wd.com/t/backup-to-mycloud-from-another-network/165307
