Time Machine does not update storage capacity

It appears to have found two sparsebundles in the path of the same name.

Catalina did not inherit the old backup. So when you upgraded to Catalina it created a new backup called Anders's iMac.backupbundle. This is the new name used by Catalina but it is still a sparse bundle.

My guess is that the command hdiutil cannot distinguish one sparsebundle from another regardless of the name change at the end.

Is the Anders's iMac.backupbundle fairly small? cf. Anders's iMac.sparsebundle

Since the sparsebundle is no longer being used by your Mac why not copy it to another drive for archive (or do a whole archive of the TC) and delete the sparse bundle. That is the best way to recover disk space.

If you really want it left on the TC.. create a new folder under Data. Something like old backup. Drag the sparsebundle to it. Not sure if you will have sufficient permissions to do this but it is worth a try. Then you can run the compact on the old sparsebundle in the new location.

Apple made a whole lot of undocumented changes in Catalina to Time Machine.

Frankly I would give TM the boot and buy a 3rd party like Carbon Copy Cloner which is a whole lot more reliable.

Sneaky Apple has designed Time Machine to back up to a special type of container on the Time Capsule called a sparsebundle file. Or, if you are running Catalina on your Mac, the special file is now called a backupbundle.

The file "expands" when new data is added to the point where it reaches the capacity of the hard drive. But......and this is the part that Apple doesn't tell you about........when you delete files from the special container, the size of the container remains the same as before......so you do not regain the space that you thought you would.

Only Apple could think of something like this.

If you do want to actually regain the space, you must "compact" the sparsebundle file or backupbundle file. This is scary for most users, because it involves using Terminal commands. More info on that here:

https://discussions.apple.com/thread/7579861

Most users find it much easier to simply erase the Time Capsule hard drive.....which only take a few minutes.. The downside to this is that you lose your backups. This is not a big deal for most users, because they never need files from weeks, months or years in the past anyway. But, some users simply cannot bear to do this.

If you are interested in simply erasing the Time Capsule hard drive and starting over again with a new backup.....my recommendation for most users......post back if you need more instructions.