What MacOS are you using? Since Catalina (10.15), you can back up to any SMB server that is continuously available. About feature additions in macOS for SMB 2 and 3 - Apple Support You don’t need a static IP if your router is correctly configured to recognize the host name you have given to the MyCloud.
From the MyCloud webgui, create a share (i.e. TMbackup) and give the mac users read/write access.
From the Finder on each mac: Go > Connect to server > smb://Username@MyCloud/TMbackup > (enter password when requested)
From Time Machine Preferences > Select Disk > (select TMbackup on MyCloud)
That is it - backups will happen when scheduled.
If you are running MyCloud Gen.1 and are comfortable to ssh into your MyCloud, you can tweak some of the config files to improve operability with Macs: SOLVED: Tweaking Samba/SMB2 for Mac & Androids - #7 by joewdex
