macOS Monterey Beta Not Install on M1 External Drive [Fixed]

if you’re using Mac device you probably heard about Apple new operating System macOS Monterey. If you’re trying to install macOS 12 on MacBook Pro, but faced macOS Monterey Beta 1 won’t install. I tried bottom troubleshooting to fix the issue but it shows  MBP13 2020 and my wife’s M1 MacBook Air and M1 Mac Mini. In this article walk you through how to install macOS Monterey on M1 external drive.

The macOS 12 Monterey size 12.2GB and after downloading a huge file installation doesn’t starts when the progress bar an error message shows that “An error occurred installing macOS 12.

macOS Monterey beta Install problems reported on Developer Side:

Can’t install macOS Monterey beta on M1 external drive
Tried to download the macOS 12 beta 1 and install to an external SSD drive connected to the Apple M1 chip Mac Mini. The installation continues until restart. The external SSD drive cannot be used to boot up.
SSD is erased and set to:
GUID Partition Map
This strategy has been used in the last few years with Intel MacBook. I wonder if this is a problem with the macOS or M1 machine?

Same here, getting: “An error occurred while setting “MacOS 12” as the startup disk: The operation couldn’t be completed. (SDErrorDomain error 108.)” when trying to boot to an external drive on M1

How to Install macOS Monterey Beta 1?

  1. Delete installer file and re-download macOS 12 and check it working or not. / Or try to re-enlisted the beta program
  2. Reset PRAM/NVRAM
  3. Reboot your Macbook
  4. Clean install macOS Big Sur and then try again.
  5. Clean install macOS On mac is time-consuming but that’s effective if you are following the step in the sequence. First Take Mac Backup in Time Machine, Put your Mac [Intel or M1] in Recovery mode and Reinstall MacOS.
  6. And now to try to boot from External drive [Safe boot mode]
  7. Turn Off turn of FileVault or Firewall/VPN, Here’s the full guide on how to Manage & Turn off VPN on Mac. Follow the steps below to quickly turn off Firewall and Start the macOS installation.
    1. Click on the Apple logo from the Mac menu.
    2. Next, Click on System Preferences option > Security & Privacy.
    3. Unlock the window and click on Turn off Firewall.
  8. Restore the firmware on the Apple T2 Security Chip.
  9. Type this command by opening Terminal.

sudo nvram IASUCatalogURL=

Please note: “You may need to enter 2 time if you got the error.”

  • After that, rerun the installer –> It worked.

    After done upgrading, you should update the nvram back:

sudo nvram -d IASUCatalogURL

Fix 10 – with boot USB for clean installation

Fix 11 – Disabling the Gatekeeper on Apple Mac, that helped me

Fix 12 – Install macOS 12 via App Store. After I tried (and failed) to install it from App Store, I found that I have a new Application:
/Applications/Install macOS 12

I right-clicked that, clicked “Show Package Contents”, and navigated to Contents -> MacOS and I double-clicked InstallAssistant.

I was able to install it from there

Fix 11– Possible error due to BridgeOS udpate issue

To resolve issue, I suggest you creating a new partition and re-install Big Sur, So Wipe the entire hard drive and make a clean install of Big Sur (macOS 11).

installing from a boot disk, installing in recovery mode, safe mode, internet recovery mode.

Last Solution– Wait for few days and try Trying the public beta profile download on your Mac

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