Can't boot mac or fix it with disk utility
If you have a backup I'd recommend formatting the drive, reinstalling macOS and restoring from backup.
If you don't have a backup you could try 3rd party tools like Alsoft DiskWarrior or Micromat TechTool to repair the volume. Alternatively you could manually back up data via Terminal or by booting from an external drive (and using Finder) if the volume still mounts.