Security Settings do not allow this Mac to use an external startup disk

Question

Level 1

4 points

Security Settings do not allow this Mac to use an external startup disk

https://support.apple.com/en-gb/HT201372

After the step "Select Install macOS (or Install OS X) in the Utilities window, then click Continue and follow the on-screen instructions."

It show the words " Security Settings do not allow this Mac to use an external startup disk"

and then I change the Security Setting (medium security , allowd boot media)

reboot system https://support.apple.com/en-us/HT208198

My USB FLASH disappeared.(SanDisk iXpand Flash Drive Luxe USB Type-C 64GB)

What steps am I doing wrong?

IMAC 27" 2020

iMac 27″, macOS 10.15

Posted on Feb 9, 2022 9:28 PM

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Answer 1

Owl-53

Level 10

101,965 points

Feb 10, 2022 2:16 AM in response to 揆一

The Bootable Installation Drive was successfully created via the method in your original posting ?

What version of macOS was made on the USB Bootable Installation Disk.

If this computer Originally came as new with macOS 11 Big Sur and the bootable Installation Media was made for an older version of macOS - this will be impossible to boot to the Bootable Installer

The Apple Licence of Use prohibits this.

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Answer 2

Owl-53

Level 10

101,965 points

Feb 10, 2022 3:20 AM in response to 揆一

Change to>> No Security

Change to >> Allow Booting from External or removable media

Or has the USB Media Drive become damaged and need to re-create the Bootable Installer of Big Sur

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Answer 3

揆一 Author

Level 1

4 points

Feb 10, 2022 3:10 AM in response to Owl-53

1. yes

2. imac 27” (2020) 10.15.7 —>made usb bootable Big Sur 11.6.1

First time USB can be seen , but after change security setting USB disappeared.

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Security Settings do not allow this Mac to use an external startup disk

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