Why doesn't my WD My Book backup drive work with Time Machine after installing Big Sur?

I found a workaround. Go to WD Drive Utilities (I had to reload this from the WD website because I had uninstalled it), then I attached the My Book USB cable to the computer. A Drive Utilities window popped up showing "attach a supported WD drive" and when I did this I got another window with the "Unlock Drive" option. I entered my password, then clicked on "unlock drive". My Book For Mac then appeared in Finder and I was able to use Time Machine. I was also able to eject the drive from Finder, which I had not been able to do under Sierra (I had to shut the computer off before detaching the cable in order not to get the "drive ejected incorrectly" message, and also previously had to restart the computer immediately before attaching the drive cable, so this method actually is better). There are so many disconnects with component compatibility these days that it's hard to make anything work unless you're a digital genius. My discovery was pure luck. Anyway, thanks for your input.

Thanks, tbird, but Disk Utilities does not give me the option to erase and/or reformat. They are grayed out because the disk is locked, and the unlock app is on the virtual disk contained within it.