Unable to boot from external USB media (M1 macbook pro)

<< Apple support told me that Apple CPU macs should allow booting from external drives by default >>

...then person you were talking to needs to be re-trained, because that is FALSE!

<< The Startup Security Utility on Apple CPU macs no longer has an option for allowing booting from external devices >>

That is also Not correct.

But it is not pushed in your face -- you must choose Startup Security Utility off the 'Utilities' Menu, as described in the article linked below, and unless/until you do, none of your alternate boot methods can work.

Change security settings on the startup disk of a Mac with Apple silicon - Apple Support

You must restart your Mac for the changes to take effect.

AppleInsider and ElectricLightCo have articles on how to do this.

Looks like a lot more hoops to jump through than in most of the Mac OS X / Intel days, because of tightened security. Also both articles recommend using Thunderbolt drives, not USB-C ones.

https://appleinsider.com/articles/21/01/03/how-to-boot-an-apple-silicon-mac-from-an-external-drive

https://eclecticlight.co/2022/11/10/make-a-ventura-bootable-external-disk-for-an-apple-silicon-mac/

https://tidbits.com/2021/05/27/an-m1-mac-cant-boot-from-an-external-drive-if-its-internal-drive-is-dead/

Startup Disk security policy control for a Mac with Apple silicon - Apple Support

Apple does not closely follow the problems posted on the forums. They can act only when a cohesive and fairly complete description of the problem is supplied. Many of these come in through Apple Support, but if you can supply a description of the issue, you can use product feedback to report this as a "bug report":

Product Feedback - Apple

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I do not believe that is CORRECT either.

You need to have a conversation with Startup Security Utility to authorize ANY booting from ANY external devices.

Then you have to have completely erased the candidate PHYSICAL drive (not just the Mountable, user-named Volume) and made it an Apple File System (APFS) drive with a mountable APFS Volume.

And only then can your Mac consider installing onto it (which has always required booting its embedded minimal MacOS, of exactly the same version as the incoming version of MacOS.

You have not mentioned ANY of these steps, or referenced the Apple article about creating a bootable USB-stick Installer, so forgive me if I seem to be belaboring what MAY, by now, be obvious to you. You have not mentioned any of the required steps.

I have a bootable Monterey Installer USB stick on hand already.

I shut down my MacBook Pro 16-in M1, and held the power button to get the Startup Manager/Options combined screen.

I chose Options.

it showed four choices, none of which was startup security manager.

I chose Startup Security Manager from the Utilities menu, and was able to select Reduced security.

Once the changes were saved, I did a shut down.

I shut down my MacBook Pro 16-in M1, and held the power button to get the Startup Manager/Options combined screen.

it showed an Admin Username, and demanded that Admin User's password.

then it continued, and showed a choice of the bootable Installer USB-Stick, the default internal Boot drive, and Options.

I chose the bootable USB-stick Installer.

it rebooted from that USB stick, then showed the ready to Install MacOS display.

It all appears to my eye to work the way the article says, and

... the agent you were dealing with needs re-training.

<< I'm not trying to create a bootable installer. >>

My example was using items I already had on hand to quickly demonstrate that booting from external devices was possible on Apple-Silicon Macs.

My new Mac was delivered to me with Ventura. I re-imaged it with Monterey, because I would rather be running Monterey. I honestly do not remember what I had to do to install older Monterey, but it was no trouble at all.

<< If Apple stopped supporting USB-C drives, >>

Nonsense.

Apple supports USB-C drives just fine. Even USB-C drives plugged into ThunderBolt ports. Still supported.

Apple supports older USB-A connectors on Macs that HAVE such connectors, such as the new Mac Pro 2023 42 lb silver tower.[Yours Mac does not happen to have any USB-A connectors.]

A simple adapter allows conversion from ThunderBolt and/or USB-C ports and use of USB-A USB-sticks.. Still supported.

I have an external SSD with bootable and working version of macOS Ventura. My Mac is currently on macOS Sonoma 14.4.1. I don't remember when I installed Ventura on my external SSD, but I partition half of the disk for Ventura, and left half for another OS.

So now I am trying to install macOS Monterey on that other half. I have created a bootable installed on a separate USD-C stick and installation seemed to work fine. But now when I try to select macOS Monterey from the startup options I get the same problem as you described with the spinning wheel and then nothing when clicking 'Continue'.

However, when I try to use it as a startup disk I get a different error:

"The version of macOS on the selected disk needs to be reinstalled."

I have already reinstalled once but that didn't seem to fix anything.

I actually got it to work.

So previously I was installing Monterey on a separate volume on the external disk, because it just seemed like the better option.

But then I tried creating a partition instead of a volume in Disk Utility and was able to boot macOS Monterey.