Why won't my Mac connect to my existing Time Machine backup?

thedust2010 wrote:

I have an M1 Mac Mini running the latest version of MacOS (13.0.1). An external hard drive is connected to the Mac Mini, with a volume set up to be a Time Machine backup destination. Many successful backups exist on this volume in a .sparsebundle file. Now the backups no longer work. Under Time Machine on my Macbook Air it says Waiting to complete first backup. When you click for more details it says:

Time Machine couldn't complete the backup. The backup disk image is already in use. Check that the image is not in use by another computer. If the image is not in use and the error persists, try rebooting the server.

When I log into the Mac Mini and try to eject the volume I get:

The disk couldnt be ejected because it is being shared. Eject the disk on the other machine or stop file sharing.1.

I've removed the volume from file sharing, but the result is the same when I try to connect to the Time Machine share from my Macbook Air:

Enter user credentials (success)

2. Prompt to use existing backups or start a new one (select existing)

3. Enter the password for the Time Machine backup (success).

Then it just hangs for a few minutes until it gives up trying to connect. The message is the same:

Time Machine couldn't complete the backup. The backup disk image is already in use. Check that the image is not in use by another computer. If the image is not in use and the error persists, try rebooting the server.

If I eject the volume from the Mac Mini and remove it from File Sharing, then the error message changes to:

The backup disk is not available. Make sure the backup disk is connected or select a different backup disk.

Why is this so difficult? Did something change with Time Machine backups in MacOS Ventura? Do I have to start from scratch and lose my backups? Given that Apple no longer sells Time Capsule, how are people doing their Time Machine backups these days?

NOTE: It's worth mentioning that the Mac Mini is backing up to this disk without issue, on a separate volume. For some reason we cannot successfully back up across the network.

What happens if you hold the Option key and click open the

TM icon in the menu bar>Browse Other Backup Disks...

If you need to create a new backup from Mac - Apple Support

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

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.