Do you have a second generation My Cloud or a My Cloud Home? They ARE NOT the same or even similar devices. A My Cloud Home IS NOT supported by OS5 and uses completely different firmware and a completely different operating system than the My Cloud line.
Single bay My Cloud looks like this:
My Cloud Home looks like this:
If you have a My Cloud Home see the dedicated subforum for that device where users more familiar with that unit may be able to assist with your issue.
Following this and other advice, I created binary files for the apps in this folder ( WDMyCloud_NAS_Apps_GPL_20201112) and apps in the wdpksrc git repo for WDMyCloud (Gen 2).
So that others don’t have to recreate the steps, below is a link to all of the apps I created.