Demonstrated 10 years ago as a major new feature in APFS, and capable of blazingly fast rollback preserving data including document versions, snapshots still aren’t fully accessible or documented.
rollback
Can be a Mac-saver if you have problems when your backup storage isn’t available. You don’t need to run Time Machine to make them, and can roll back in Recovery, as shown here.
If it’s so easy to uninstall a troublesome RSR, why can’t we simply roll back to a previous version of macOS, like we did in High Sierra?
Snapshots are designed to make it easy to roll back to a previous state. Why then can’t you use a snapshot to roll back to an earlier version of Big Sur?
The Eclectic Light Company 