That error occurs when you attempt to run an old out-of-date copy of the installer.  Steps to correct:

  1. go to your Applications folder and delete the items that start with Install macOS (followed by Mojave or similar) - delete them all if you have more then one
  2. close the app-store and re-download the desired macOS version using the provided links
  3. the up to date copy will work until Apple releases a new version of macOS - e.g. 10.15.8 at which point the old version will generate the error of this copy of the Install macOS is damaged or similar so they are always time-sensitive, but impossible to predict what the amount of time will be