Can the MacOS be repaired without loss to personal files

Yes. If you boot into Recovery mode and select "Reinstall macOS" your files will not be deleted.

You would have to erase the drive using Disk Utility IF you wanted to erase your files before reinstalling.

Here's a link to booting into Recovery Mode: https://support.apple.com/en-us/HT201314

Good luck!!

It is a sane thing to have a Time Machine backup of your Mac before attempting any operating system changes, whether they do or do not impact your home directory.

👍

Couldn’t agree more with VikingOSX - always have a backup (or TWO!) before you make ANY major changes!