How can I create an OS X 10.11 bootable installer successfully when I am greeted with a message saying “This version of OS X 10.11 cannot be installed on this computer” on my Mac?
You’re making the external hard drive a bootable installer instead of installing this OS X 10.11 on your Mac, so you should store the OS X 10.11 on the target hard drive then you can use it to boot other Mac devices. Compared to making a bootable installer by yourself, you can download the OS X 10.11 ISO file to the hard drive directly, which is much easier and simpler:
Free Download OS X 10.11 ISO file
Then you can boot your Mac from the external hard drive:
Boot an Intel Mac from the external drive:
- Restart the Mac and immediately press and hold the Option key.
- Release the key when you see the Startup menu.
- choose the external drive with the wanted macOS to boot up.
Boot an Apple Silicon Mac from the external drive:
- Turn off the Mac completely.
- Press and hold the Power button until you see a list of bootable drives.
- Click the external hard drive to boot the Mac from it.
If you want to set the external drive as the default startup disk, you can make it from the Apple menu > System Settings, click General, select Startup Disk, then choose the external drive under “Select the system you want to use to start up your computer” and click Restart.