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.

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.