If you do a forum search you’d see this is discussed often with very few options.
There are several options, here are a few.
- Use WD Sync.
- FTP, but note that FTP is NOT secure.
- Install the unofficial CloudDAVMod program and remote map the My Cloud then use a backup program on the computer to backup to the mapped My Cloud.
https://community.wd.com/t/app-clouddavmod-v1-0-for-firmware-v4-05-2016/161543
Some past threads that may have more information:
https://community.wd.com/t/backup-to-remote-my-cloud/94890
https://community.wd.com/t/remote-time-machine-backup/91087
https://community.wd.com/t/backup-to-mycloud-from-another-network/165307
https://community.wd.com/t/sync-back-up-3-different-locations/164417
