Because Time Machine maintains an active state on volumes it uses, you may need to disable Time Machine (in System Settings > General > Time Machine) in order to repair a backup volume.

Every time the user is in one of those programs, the whole 20 GB virtual image or whatever is changed, and TM backs it up. I know you said they only use 9 GB, so maybe not.

Apple's Time Machine is an invaluable tool for backing up your Mac data and personal files - here's how to get started with the feature.

My backup strategy with my main Mac has been to use a networked Time Machine backup and also a Time Machine backup to an external HDD that I connect perhaps a couple of times per month. So far ...

It's not just Intel code — after a period of undeath, Time Capsule's time is coming, with Apple cutting off support for Time Machine backups using the hardware in macOS 27.