You may want to post (or see) the dedicated OS3 My Cloud Mirror subforum where users more familiar with that device may have additional answers or suggestions.
OS3 My Cloud Mirror
https://community.wd.com/c/personal-cloud-storage/wd-my-cloud-mirror/110
One can try to run the OS3 “patch” suggested in the following thread.
Unofficial Patch for OS3 Zero Day RCE Vulnerability
https://community.wd.com/t/unofficial-patch-for-os3-zero-day-rce-vulnerability/268631
One should also see if their local network router/firewall can block inbound/outbound broadband traffic to the My Cloud in addition to the various steps you’ve already taken. There are many other steps one can and should take to harden their local network to prevent general intrusion.
