How to reinstall OSX without losing data

Boot into the Recovery volume (boot with the Command + R keys held down  - Intel Macs) or  (How to Boot an M1 Mac into Recovery Mode) and reinstall the system. This will not affect your user data.

However, as with any major update, upgrade or repair you should have a current and full backup of your boot drive.

Back it up and reinstall the OS normally. The OS reinstall won't affect your data unless an issue occurs, but other things can.

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Why do you want to reinstall the OS?

It is mounted read-only from a sealed snapshot that only Apple can modify.

Reinstalling the OS won’t change anything.