Getting Error -69624 while trying to delete/run first aid on a Time Machine backup disk after the Time Machine was unable to complete a backup

Narad wrote:

While troubleshooting the above problem, the disk became unmounted.

What finally solved the problem was to create a new partition with the size of the entire disk. That erased the volume along with all the data in it. I was not bothered losing that data as I had a duplicate Time Machine backup disk.

I added the disk back to the Time Machine.

For whatever it is worth, it is an HDD.

thx Narad for your work-a-round

If you value your user data

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

More than one device, more than one backup methodology.

new Back up your Mac with Time Machine Ventura — https://support.apple.com/100195