sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume install mac os on external hard drive
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. sudo /Applications/Install\ macOS\ Big\ Sur
Carbon Copy Cloner (free trial, highly recommended) or SuperDuper! (free version available). running legacy software
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume (Change “Sonoma” to “Ventura” or “Monterey” as needed)