Cannot access my cloud data via file explorer

What specific My Cloud device do you have? The My Cloud Home is a completely separate device with different features/options than the My Cloud line. If you have a My Cloud Home, see the subforum for your My Cloud Home model.

https://community.wd.com/c/home-cloud-storage

One thing to check when using Microsoft Windows. Ensure SMB1.0 is enabled. Microsoft disabled that option in recent Windows updates and in new Windows installs.

Other things to check in Windows.