Unable to downgrade my MacBook Air to macOS Monterey

There are more than 2 ways to achieve what you want to do Before you " want to give them a virgin Mac. "

Reset your Mac to factory settings to prepare it for a new owner.

The other way >> Scorched Earth Method 

This method will WIPE ALL Data and there is No DATA Recovery - Period.

>> Only works on Intel Based Apple Computer <<

To perform this action will require booting from a Bootable Installer. 

The Bootable Installer can Only be performed on an Apple Computer 

This will have to be performed from a Qualifying Computer to run the version of macOS to be made on the Bootable Installer.

Example : Bootable Installer of Monterey would have to be done on a computer that Qualifies to run Monterey.

Notation: If the computer being used to perform this action is Too New or Too Old to qualify to run the version of macOS - this computer can’t be used.

Alternative is, to gain access to a Qualifying Apple Computer from a family member, friend or associate.

Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.

Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive. 

It will present options >> Disk Utilities >> View >> View ALL attached Drives. 

Choose the Upper Most Drive ( not the volumes indented and list below ).

The drive normally is called Apple Media or Apple SSD - that is the drive to Erase and format as APFS with the GUID Partition Map.

Once that is done >> backup out of Disk Utilities and choose install macOS. 

Follow the prompts and it may automatically reboot several time. 

Upon a final reboot - Setup Assist will present with the newer version of macOS.

Stop at that point

Just Turn OFF the computer using the Power Button

The next time it is Turned ON, the new Owner will be presented with Startup Assist

This is where I am getting confused

The question " Unable to downgrade my MacBook Air to macOS Monterey "

It appears to imply this computer has a newer version of macOS other than macOS 12 Monterey ?

When I check the what a 2015 MBA qualifies to run

macOS 12 Monterey is the Best it could possible run

macOS Ventura is compatible with these computers

So if you were to use the previous suggestion and use Internet Recovery Mode >> Option ⌘ r

You could Wipe the Drive 100% clean and reinstall ( hopefully ) a clean version of Monterey

No fuss, no USB Installer etc

wbowles wrote:

Got message 'Operation couln't be completed. (com.apple.Buildinfo.preflight.error 21.)

Shall end here with this suggestion

Have the computer evaluated by the Professionals who have the Special Hardware Software and Expertise to diagnose the issue and offer possible solutions

Make an Appointment at the Apple Genius Bar or call 1 800 MyApple and have them evaluate the computer

Other location Call Centres 

 Contact Apple for support and service

wbowles wrote:

Yes, that's the problem, I don't have a bootable installer, if I did, we wouldn't be having this conversation. I've tried to create one on a USB stick, without success and the only bootable drives I have, have an even earlier OS on them.

@ wbowles wrote " I have a version of Monteray (as a DMG file) on a 128Gig USB, version unknown. "

I do not know how or where this .DMG file of Monterey was made or from where it was downloaded

I say this because the Last .DMG if a Full Version of OS X / macOS made available from Apple was for OSX 10.12 Sierra released somewhere in 2016

Full Versions of macOS, starting with macOS 10.13 High Sierra and above, all come as Compete and Self Contain Installer Applications

wbowles wrote:

I'm NOT trying to recover the drive! I want to erase the disk and reinstall Monteray! I'm giving the Mac away and want to give them a virgin Mac.

The last thing I'll point out on the subject. From the link.

"You can use the apps in macOS Recovery on an Intel-based Mac to repair your internal disk, reinstall macOS, restore your files from a Time Machine backup, set security options, and more."

" Command-R: Start up from the built-in macOS Recovery System. Use this key combination to reinstall the latest macOS that was installed on your system, or to use the other apps in macOS Recovery.

Option-Command-R: Start up from macOS Recovery over the internet. Use this key combination to reinstall macOS and upgrade to the latest version of macOS that’s compatible with your Mac.

Option-Shift-Command-R: Start up from macOS Recovery over the internet. Use this key combination to reinstall the version of macOS that came with your Mac or the closest version that’s still available."

There is nothing about having a bootable installer mentioned.

Good luck.

See: How to reinstall macOS - Apple Support

Here: Use macOS Recovery on an Intel-based Mac - Apple Support