How to set up WD 6TB My Passport for Mac as a Time Machine backup drive on Sequoia 15.4.1?

When you plug it in, Time Machine may ask you if you want to set it up.

If it doesn't, open Time Machine and add the drive by clicking on the Add button.

Back up your Mac with Time Machine - Apple Support

I recommend that you first reformat the WD disk using the Disk Utility app - not any maintenance app that came with the disk. It will likely cause problems and should be Trashed. Then you can set up Time Machine as pe its instructions.

hockey2014 wrote:

I followed your instructions. It started back up but stopped with an error message-Disk Not Ejected Properly.

I unplug the cables & reinserted & did a restart. I got the same result. It started backing up & stopped with the same message.

Is your Mac going to sleep while it is backing up? Make sure it isn't set to put hard drives to sleep.

Do you have any other ideas to help solve this issue?

As Ronasara suggested, perhaps just try formatting the drive.