I’m in touch with WD although response time is pretty slow (every 5 days or so).
I’ve posted their first suggestions here: link
Second answer was this:
Therefore, you have to follow the instructions of the same link already sent on the 1st email to correctly configure Time Machine using Samba (SMB)
Initial Time Machine Backup Failed or Could Not Complete
My Cloud Home: macOS Time Machine Error “Backup Disk Not Available”
Unfortunately even these solutions mix up OS5-devices and My Cloud Home. Or does anybody e.g. know how to adjust TM maximum size in My Cloud Home preferences?
