Monterey 12.3 doesn't install on an external SSD

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Monterey 12.3 doesn't install on an external SSD

I'm on a 2019 16" MBP. I downloaded the App Store Monterey 12.3 installer. I ran it onto a bare 1 TB external SSD. It seemed to load onto the drive correctly, and at the completion the system rebooted. Normally it them proceeds with the installation. Instead, the system booted into the internal drive. The drive appears to have the system on it. I tried booting with the Option key, but it doesn't see the external drive. However, once booted into internal, I can go to Startup Disk, and it sees the external as a startup volume.

I can select it, but when I try to restart I get this error message.

I've tried this a few times on a couple of drives with the same result. This is pretty ridiculous, extremely frustrating, and a complete waste of my time.

If anyone has any idea what the problem might be, or how it can be remedied I'd very much appreciate some help.

Thank you for any assistance.

Posted on Mar 21, 2022 7:19 AM

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Answer 1

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PRP_53

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85,459 points

Mar 21, 2022 7:31 AM in response to Tom Wolsky

Judging from Original Post and pic included the computer on which this is being attempted has already been upgraded to Monterey ?

Reason for asking >> There are reports appearing on the ASC Forums regarding failed installation of Monterey on older Qualifying Apple Computers. In most cases this is related to having a NON Apple Original internal drive ?

In your case the External Drive, not being an Apple Original Drive would come into play.

The EFI Boot ROM included in Monterey is verifying for Original Apple Drive and if not found , may Balk or fail to upgrade to Monterey.

Reports indicate the EFI BOOT ROM is Required to Flash the Computer and is a requirement for a Successful Monterey Installation.

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Answer 2

PRP_53

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Mar 21, 2022 7:25 AM in response to Tom Wolsky

Does the 2019 16" MBP. have the T2 Chip ?

Extra Special Notation regarding the Touch ID equipped Apple Computer.

About Startup Security Utility and Must Enable from Recovery Mode the ability to boot from External Drive .

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Answer 3

Tom Wolsky Author

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Mar 21, 2022 7:58 AM in response to PRP_53

Thank you very much for the explanation. That's very unfortunate. It's the first build since the 90s that I have not been able to install on an external. This seems to be Apple's plan going forward. It will pretty much end my participation in being able to work with system installations for testing.

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Answer 4

Tom Wolsky Author

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151,089 points

Mar 21, 2022 7:27 AM in response to PRP_53

Yes, it does. Security is set to Moderate to allow external boot drives. I've done it for many OSs prior to this build.

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Answer 5

PRP_53

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85,459 points

Mar 21, 2022 8:03 AM in response to Tom Wolsky

As person of such Long Standing and Reputation on these ASC Forums will no doubt find a solution come what may.

You are welcome and thank you too :-)

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Answer 6

PRP_53

Level 10

85,459 points

Mar 21, 2022 8:07 AM in response to Tom Wolsky

There is alway to Clone Existing Monterey to External Drive using the " Legacy " method in Carbon Copy Cloner and run the Test from the External Drive.

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