Is this a legacy product now that WD have done something with My Discovery? I bought it last year as a backup device for OS 10.15.7 (Catalina), but it is no longer being recognised as a backup device.
Do you have a My Cloud? If not, you may want to move or post in the correct subforum for your device. This subforum (My Cloud) discusses a completely different WD device, a network attached storage device which is not an external USB hard drive like the My Passport.
WD External Drives