Trying to revive Time Machine

The Time Machine shows a .sparsebundle file that won't open.

I started to follow the steps from Encryptor5000's post 12/24/2022:

1. Open Terminal, located in Applications -> Utilities.
2. In Terminal, type "hdiutil attach" (without the quotes), and add a space.
3. Locate the sparsebundle disk image in the Finder, then drag and drop it onto the Terminal window. This should automatically provide the filepath to that image.
4. In Terminal, add a space after the image path, and type "-nomount" (again without the quotes). Hit Enter/Return.
5. If asked for the image password/passphrase, enter it when prompted. Terminal won't show you any characters as you provide the password.
6. If successful, the image should be attached, but not mounted. Terminal should print out a list of partitions on the image. At this point, quit Terminal and open Disk Utility.
7. In Disk Utility, select the volume inside the image (the most indented entry under the disk image), and run First Aid on it.
8. If that succeeds, run First Aid on the next layer up (either an APFS container, or the virtual disk itself). Keep going up until you have ran First Aid on the virtual disk (top layer) itself.
9. If all passes of First Aid succeed, select the volume inside the image (bottom entry), and click Mount.
10. If successful, the volume should mount, and it should now be accessible as normal in the Finder.

I made it through Step 7, although there was no volume inside an image - just a single list item. I ran First Aid on it. It took several hours. In the end, the process failed.

I tried again, but this time, I did not get to Step 6; after Step 4, Terminal said the attach failed because the disk was "unavailable."

Get Info says the Image Bundle is 530 GB, created Jan 2012.

I'm using Sonoma 14.5, Disk Utility v. 22.6