kaydeedid wrote:
I have been using a WD external Drive as my time machine backup drive. It worked fine until I upgraded the system to Monterey 12.1, Now, it no longer backups my computer. I have erased the drive and tried troubleshooting, but I can't figure it out
The drive should be reformatted as APFS/GUID for Monterey Time Machine.
As Jeffrey indicated, first open Time Machine Preferences, remove the drive from Time Machine, then open Disk Utility and erase/reformat the drive as as APFS/GUID. The entire drive should be dedicated to Time Machine, don't create other volumes or partition it for other uses. Then open Time Machine Preferences again and designate the blank drive as a Time Machine drive and start a backup.
Also to check: make sure you do not have WD utilities of software or firmware installed. If so, completely uninstall it. You may even have to use a program like Find Any File to locate all residual WD files (which may have a name that contains the "WD" or "WDC" character string) and remove them. Others have reported Time Machine malfunctions when they had such tools or software installed.