Time Machine backup Ex4100, and Time Capsule

Can Time Machine backup data from My Cloud EX4100 NAS to a Time Capsule

I don’t think Time Machine allows you to select the My Cloud as your source backup drive. Let’s see if other users can share some knowledge here.

No it can’t. Why you want to do that?
You can specify both drives (EX 4100 and TimeCapsule) as destinations for you backup on the mac.
The mac then backs up to both, whichever is available.