Downgrade MacOS without second mac (M1)

I've successfully downgraded my mac when it softbricked, the solution was not easy to find. That's why I'm posting all-in-one tutorial here.

After flashing MacOS 12 (Developer beta) I've experienced issues with my XCode and homebrew. I needed to go back asap, beacause I need XCode for my school project.

I was dumb enough to not download big sur from app store while I was on the MacOS 12, I directly went to restore mode and erased my disk...

Then I discovered that I can't choose which MacOS version I will install, the only option was to reinstall the developer beta one.

After installing it again I was not able to create account, so I softlocked myself. Without a second mac I couldn't make a installation USB.

Downgrade from MacOS 12 to Big Sur

  1. Turn off your mac and then hold the power button until the "options" button shows. Click on it.

  2. Erase the main disk using disk utility

  3. Connect a removable drive (could be SSD or a USB Flash drive)

  4. Enter the following commands in the terminal

    • cd '/Volumes/<name of your removable drive>'

    • mkdir -p private/tmp

    • cp -R '/Install macOS 12' private/tmp

    • cd 'private/tmp/Install macOS 12

    • mkdir Contents/SharedSupport

    • curl -L -o Contents/SharedSupport/SharedSupport.dmg

    • ./Contents/MacOS/InstallAssistant_springboard

  5. Something strange will happen. It looks like you are reinstalling beta version, but actually it will install Big Sur.

  6. After Installing it, turn off the computer and go back to the recovery options

  7. Open terminal and enter:

    • resetpassword
  8. Dialog window will appear, in the bar select erase mac and then confirm it (blue link)

  9. Computer will reboot back to restore mode.

  10. Install our "fake" big sur again

    • cd '/Volumes/<name of your removable drive>/private/tmp/Install macOS 12'

    • ./Contents/MacOS/InstallAssistant_springboard

  11. After installing you can finally log in and create recovery usb (You need to reinstall the system again to get rid of "Reinstall MacOS 12" in the recovery menu)

Thanks to 2023