You now have a portable, bootable Mac environment. Whether you’re testing a new OS, running legacy software, or simply keeping a disaster recovery tool in your bag, this setup puts you in control.
Carbon Copy Cloner (free trial, highly recommended) or SuperDuper! (free version available). install mac os on external hard drive
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume You now have a portable, bootable Mac environment
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume (Change “Sonoma” to “Ventura” or “Monterey” as needed) You now have a portable
sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume