I would like to back up Gnucash to a external hard drive. Latest Gnucash version and latest Mac OS 10.12.6.
To backup the actual application: Copy it from the Applications folder to the backup location.
To backup your ledger: Open you ledger, then select 'save as' and save it to a different location. Make sure when you open it again, you explicitly go to 'open' and open the non-backed up version or Gnucash will pick the last saved file to open (the backed up version). Alternatively, you can just copy the files and logs from the original directory to a backup location.