Updating is so much safer now

At worst, macOS updates could wipe everything stored on your Mac. Because the system files were copied into the same volume as your apps and Home folder, when anything went badly wrong, the whole volume was at risk, and sometimes had to be wiped for a full reinstall.

Catalina started to change that, and now in Big Sur and Monterey, macOS installs and updates are largely performed with the separate Data volume unmounted. Even if the installer completely messes up the System volume, you just enter Recovery and reinstall macOS.

Your precious Data volume should then be reunited with a fresh System volume, and carry on without loss of a single bit from your files. If you thought the Sealed System Volume was just about security, you’re seriously underestimating its value.