What you need to create a bootable installer
A USB flash drive or other secondary volume formatted as Mac OS Extended, with at least 14GB of available storage
A downloaded installer for macOS Big Sur, Catalina, Mojave, High Sierra, or El Capitan
Download macOS installer image from my shop or App Store.
If you download macOS installer not from App Store you nead open the downloaded image,then copy Install macOS [version name] to Applications.
If you are using an existing thumb drive, make sure to backup all existing data inside as we are going to format the thumb drive, getting it ready and compatible for the bootable mac installer.
Plug the thumb drive into the USB port of your computer.
Launch Spotlight (Command + Space), type in “Disk Utility” and hit Return to launch the app.
Look for the name of your thumb drive under the “External” section on the sidebar of Disk Utility App.
Click once to select your thumb drive, then click the “Erase” icon on the top.
Give it a name, or just use “Untitled“, make sure the format is Mac OS External (Journaled), then click the “Erase” button below.
To proceed, you will need to ensure the downloading of the macOS installer (step 1) has completed.
Launch Spotlight (Command + Space), type “Terminal” and hit return to launch Terminal app.
Copy one of the command below that matches your criteria, replace to your thumb drive’s new name and paste it inside Terminal.VOLUMN_NAME
Big Sur installer
sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/VOLUMN_NAME
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/VOLUMN_NAME
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Yosemite.app
sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Mavericks.app
Hit Return after confirming your command.
Enter the administrator password and hit Return again.
Type “Y”, and hit Return to confirm erasing your thumb drive to begin the process of creating a bootable thumb drive.
When you see “Install media now available at…." in Terminal, that means the entire process is done.
You can then Eject your thumb drive and quit the Terminal app.
If you have managed to follow through till this step, this means you have created a bootable thumb drive with macOS installer. Now, let’s give it a test to see if it works.
Plug in the thumb drive into the USB port of a compatible mac.
Restart your computer.
Hold the Option key when your computer starts to boot.
If you see a screen that provides you with boot options (like the screenshot below), that means you’re bootable thumb drive is working.
Double click“Install macOS …” to install your Mac afresh.