I have a White WD MyCloud 4 TB and it is port forwarded. I can’t access my WDMyCloud on files.mycloud.com but I can access with my Android phone using My Cloud app outside my home. I just want to access files on my Computer
Have you tried turning Cloud Access off and back on again? This forces MyCloud to re-stablish a connection with the WD connectivity servers. This connection can fail (silently, i.e. MyCloud continues to report a good port forward connection) if your router is assigned a new global IP by your ISP.
If all you want to do is access the file server local to your network, then you are far better off simply mapping the device into your file system. You do not need to use any MyCloud app or remote access portal to access files local to your network.