WD removed the ability to remotely map a My Cloud Share more than two years ago. I don’t think it was ever an advertised feature (either on the box or on the website). Instead was a undocumented feature available from the old WD2Go.com website.
To connect to a remote My Cloud one has the option of using; FTP (insecure), MyCloud.com, My Cloud mobile apps (iOS and Android), WD Sync, or the WD Desktop application that is end of life (no longer supported by WD).
Remote access/Cloud Access is a bit fickle with this device. Sometimes one has to access the My Cloud Dashboard > Settings and disable Remote Access/Cloud Access. Wait a few minutes, then reenable it. In some cases one’s broadband provider may block remote access to the My Cloud which forces the My Cloud user to reconfigure the My Cloud Remote Access setting to Manual and change the two ports used for remote access. When one does that they also need to setup port forwarding within the router the My Cloud is connected to so the router forwards the two new ports to the My Cloud IP address.