did you try to edit the drive hidden state only on computer ?
It's highly possible that your computer, or antivirus, is blocking MBR or GPT edition and revert it. it can be seen as a virus trying to alter your drive.
Did you try tools directly on your console ?
Like XploitU suggested, you can try this "WiiU homebrew" :
https://apps.fortheusers.org/wiiu/USBHide https://gbatemp.net/threads/612871/
be sure to unplug any WiiU HDD when trying, just to be sure.
or
this "Wii homebrew" (in vWii mode, or on a real Wii) : USBToggle, from the Ustealth original thread first post
https://gbatemp.net/attachments/usb_toggle-zip.9038/ https://gbatemp.net/threads/ustealth-wii-u-format-disk-nag-workaround.352786/
@Xpl0itU didn't know your tool.
I added it to Ustealth's first post thread