Unable to boot Macbook M4 from new external drive.

TWPotter wrote:

Macbook M4 Pro. Sequoia 15.2

External disk is Samsung T-9 (4T)

Boot/recovery/Security was set to reduced security. No “boot from disk” option in menu.

Erase disk (expanded menu, erased from top of disk).

Formatted APFS with GUID partition.. Name is 7 characters with no spaces or special characters.

Run OS installer from boot up recovery. Install to external disk.

Upon reboot external disk shows volume on disk as “Bootable = Yes" in Disks.

When rebooting and selecting the drive, it spins for a moment and then no change.

If I go to options, select startup disk, I get an error. “The selected version of macOS on the selected disk needs to be reinstalled”.

Upon reboot, looking at the external disk I see the system folders.

My first Macbook and first attempt booting from external disk. I've tried many times. I'm missing something here.

I have also tried this with different SSD drives, different cables, and connected to different ports. Same results.

use an external startup disk, see if this gets you any further

M-series Mac

ref: Change security settings on the startup disk of a Mac with ...

Select ”Allow booting from external media.” 

TWPotter wrote:

I have updated the Security Settings for the internal disk. There is no "Allow booting from external media" option in the menu (same as image in linked document).

Yep that seems to be more applicable to the T2 chip...

See what electric light has to say—

https://eclecticlight.co/2024/03/15/apple-silicon-6-security/

further—

Call Customer Support  (800) MY–APPLE (800–692–7753)

or on line  https://getsupport.apple.com/

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