Downgrading a MacBook Air M1 from macOS 11.3 to 11.2.3

Ahh, Updates. New functions, less bugs (or at least different ones), all wonderful. Updating is a good idea.

Unfortunately life is full of more urgent problems and sometimes one misses the given time window to stop depending on legacy function calls.

I had that issue with a software I absolutely depend on and so I decided to downgrade my first generation MacBook Air M1. After learning that a downgrade is not really foreseen, I thought: If I delete the disk in the recovery mode (when the Mac is switched off, press the on button and hold it for a few seconds to go there), I can reinstall the macOS version the device came with.

Alas, I could not. Somehow the reinstallation procedure downloaded the newest macOS version available, so I had deleted everything for nothing.

I called the very friendly, competent and helpful macOS support. The people there understood my problem and took quite some time to solve my issue, but were also new to the problem (this is the first major release that comes as an update for the new M1 machines) and promised to call me back tomorrow with a solution.

In the meantime I looked around a little further and found one myself and I want to share it with everybody, so that you dear reader will have less trouble than I did.

1. Backup your data
2. Try out your backup
3. Erase your disk in the recovery mode as described in the Apple help text HT212030
4. While following the instructions in help text HT211983 at the very end below the headline "Or use Terminal to reinstall " pay attention to this:
   1. The URI in the last line determines the version that you will install
   2. The URI for different versions of the InstallAssistant.pkg is published in a table at MrMacintosh
5. When you are done with the installation and the first reboot is happening, switch your wifi off and insist that your computer is offline.
6. Check under  -> About this Mac -> Software Update… -> Advanced that macOS updates won't be installed automatically
7. Pay attention to not install them by accident, macOS will nudge you and preselect the OS updates.
8. Connect your Mac to the wifi.
9. Talk to the authors of the software and ask what you can do so they will support the new OS version

That's it. Hopefully it will save all of you more time than I wasted on this topic.