Time Machine backups made by Catalina are not compatible with earlier versions of macOS such as Mojave. Here’s how they have changed.
backupd
When you find one, bugs will necessarily be multiple. If you think you’ve found one, you can be fairly confident that you’ll find more. Four bugs in macOS for the price of one.
Adds support for local snapshot statistics, Dark Mode, fixes a bug, and is now notarized for your added security.
Detailed comparison of how Time Machine backs up HFS+ and APFS volumes, including its use of local snapshots, with diagrams.
Found in Sierra, but seems to have fallen into disuse, and not found in High Sierra.
Found in Sierra, but seems to have fallen into disuse, and not found in High Sierra.
A detailed examination of what happens during the first few minutes after starting your Mac up. Vital for anyone trying to diagnose problems in that period.
How to run one-off backups, how to cancel automatic backups, and how to set your own backup schedules.
When Time Machine seems to take a long time preparing the next backup, or gets stuck, here is how to diagnose and deal with it.
macOS Sierra doesn’t run periodic backups using a simple mechanism. Here’s the story in full detail.
The Eclectic Light Company 