Downgrade M1 MacBook Air from Tahoe to Sonoma

That is a difficult process, especially for restoring your data since the system must be erased. There is no simple way to downgrade the system. You will need to first need to make sure you have a good backup of the data on your computer, create a bootable macOS USB installer, then boot the USB installer, erase the "Volume Group", install macOS, then restore your data from a backup made prior to upgrading to Tahoe since some data from Tahoe may not be compatible with older versions of macOS.....that is why restoring data after a downgrade is extremely difficult.

You may find it easier to attempt to fix whatever issues you are having with Tahoe. If you explain the issues you are having with Tahoe, then perhaps some forum contributors can help resolve those issues. Some of the biggest issues encountered are with third party software being incompatible & needing updates to work properly....and sometimes people just have troublesome apps installed which cause more trouble after an OS update patch or major upgrade.

To solve system performance issues or system stability issues it is usually helpful to run the third party app EtreCheck and posting the complete report here so we can examine it for possible clues.

How to use the Add Text Feature When Posting an EtreCheck Report - Apple Community

User Risk Assessment: macOS Downgrade Procedure

Before initiating any downgrade from macOS 26 (Tahoe) to an earlier version such as macOS Sonoma , assess the user’s tolerance for potential risks. The following checklist must be completed before proceeding.

Primary System Dependency

Determine whether the affected Mac is the user’s primary or only computer.

If the user cannot function without this system for several days in the event of a failed downgrade, the risk level is high.

The downgrade should be postponed or avoided until proper contingency measures are established.

Availability of a Secondary macOS System

Confirm that the user has access to another Apple computer currently running macOS 15 or macOS 26 (Tahoe).

This secondary system must be capable of performing a Revive or Restore operation on the target Mac’s firmware if required.

Lack of a secondary Mac significantly reduces the ability to recover from firmware corruption or boot failures.

Firmware Compatibility and Secure Enclave Risks

Be aware that upgrading to macOS 26 (Tahoe) likely includes a firmware update affecting the logic board and Secure Enclave Processor (SEP).

Downgrading to an earlier version (e.g., Sequoia) may or may not introduce firmware mismatch issues, leading to instability or loss of functionality.

Backup Integrity and Recovery Preparedness

Verify that the user has at least three complete backups created before the macOS 26 (Tahoe) upgrade.

Implement the 3-2-1 Backup Strategy:

3 total copies of essential data

2 different backup methods or storage media

1 copy stored offsite (for protection against natural or human-caused disasters)

Each backup should reside on a dedicated, single-purpose external drive.

For enhanced backup and cloning capabilities beyond Time Machine, refer to:

🔗 https://bombich.com

Recommendation Summary

If the user answers NO to any of the above questions:

Downgrading the Mac is not recommended.

Proceeding without proper contingency plans, verified backups, and recovery tools may result in:

Data loss

Firmware corruption

Secure Enclave failure

Complete system inoperability

carleton290 wrote:

Didn’t have a problem once I realized I should have used the computer to be downgraded to set up the bootable external drive …. My M4 iMac couldn’t set it up because it wasn’t Sonoma compatible.. Connected the drive to the MacBook, ran the terminal command and voila!

next, did the recovery process, selected the bootable drive with Sonoma and done…. Only hiccup was that Inhad a hard time with the process where I was told to select a WiFi to continue.. no selection was availabe until Inrealized that the WiFi pull down menu (just a little icon) had to be selected ..

‘install finished after about 35 minutes or so….

‘now to install Finale, a sheet music program that is not fully compatible with anything past Sonoma and marginally with Sequoia…

The computer was fortunate to survive this downgrade

As Apple does not support downgrading and especially on Apple Silicon machines

It does come with a High Risk Factor

I do see a day when this downgrading of Apple Silicon could become much more completed than the current procedure if not possible at all

Thank you for the update and have a great weekend