Downgrading macOS from Tahoe to Sequoia: User accounts, Time Machine, firmware

You seem to be getting a lot of grief and actually little help.

Because MacOS is (at least under the hood) a Unix system and has UIDs/GIDs, how do I make sure that when I recreate the accounts on my system

Create them in the same order in which you originally created them. macOS will start the first user at 501 and increment each one by one.

If you can’t remember, you can use Directory Utility to determine the UID of each one. You can also use the id command in Terminal. But, see answer to 2., below.

2. There should be no need to restore my personal files from Time Machine, as I will (hopefully) not need to wipe the external drive to reinstall Sequoia.

But I will need to restore everything that was placed on the internal disk. Is there a safe way in Time Machine to restore ONLY those files, as opposed to doing a COMPLETE restore of everything in the backup?

Time Machine restore is actually using migration assistant, from which you can choose to restore existing accounts, fully, which resolves your first problem, and you can choose whether or not you restore applications and other system data. It will not migrate anything from the external drive. If you have moved your home folder to the external, I have no idea what will happen. It may migrate all of the data from that account t into the internal drive. I would never move my home folder like that, so have no experience.

3. I have seen concerning reports from high-level contributors here that the upgrade to Tahoe involves an (apparently transparent) firmware upgrade. Does that upgrade need to be reversed, and if so, how? (That's an area where I would greatly appreciate a detailed procedure.)

I don’t know if that is an issue or not. It certainly may be possible. Apple had at one time published an article on how to revert to a previous macOS version. I cannot find that anrticle anymore which may indicate they don’t support that in all cases anymore. That could be related to all of the firmware changes that they introduce with each new macOS version. It also may be that I just can’t find the article anymore because when searching for stuff on Apple site you have to know a lot of the keywords to make it match.

Will you run into problems? Quite possibly. Some of the useful advice you’ve been given is be ready to do a DFU reset/restore. If you have an Apple Store with a genius bar nearby, they should be able to do it for you, but I don’t know if they will do it for a Sequoia installation.

From my limited experience with Apple Configurator, you need to be running the same macOS version on the Mac you use to reset DFU.

As to the installer not working from the applications fielder, it will work for the purpose you need which is creating a bootable USB Installer. That is how you must proceed to revert to a previous macOS version.

elisatems wrote:

how do I make sure that when I recreate the accounts on my system (of which there are several), they all have the same UIDs/GIDs as currently? Is it possible to specify those parameters when creating a new user immediately after an OS install?

My experience has been that if you run Setup Assistant on first boot up, after completely erasing and doing a fresh install of Sequoia, and before creating any users, then Setup Assistant (which is a special version of Migration Assistant) brings over the same users from the Time Machine backup with the same UIDs and GIDs.

This is based on my experience using Setup Assistant to migrate to a new computer from an old one. Your erased/formatted Mac will be essentially like a new Mac running Sequoia. The backup you will be using for the migration needs to be a backup made under Sequoia. In that case this is like using Setup Assistant to migrate from an old Mac on Sequoia to a new Mac on Sequoia.

I am trying here to answer your question about UIDs and GIDs. However I myself would NEVER attempt the downgrade from Tahoe to Sequoia. My Mac is a 2019 Intel 16" MacBook Pro and I have watched it install firmware updates in the process of upgrading from Sequoia to Tahoe and subsequent Tahoe updates. I cannot imagine that a Sequoia MacOS would work properly with MacOS 26 firmware. So you would also need to perform a DFU procedure to revert to Sequoia firmware. That is something I would not endeavor to execute myself but other users here can provide instructions, which are not simple.

Apple does not support downgrading the MacOS. If you ask Apple to help install a MacOS, Apple will wipe the drive and install the latest version of Tahoe 26, which will then present you with Setup Assistant on its first boot up, like a new computer. This would not be a waste of your time as there is a chance your audio issues will be gone when such an install is performed, before other stuff is installed. That might provide you with other options. Worst case scenario, you would have the option to re-erase the drive and try the Sequoia install route.

weeklycod wrote:

go to App Store search sequoia then install, go to system settings and it will update latest Sequoia and it will restart to Sequoia. it Is made by apple

This is very, very wrong.

You cannot install an older macOS version over a newer one. You must first erase the drive entirely.

Also, that does not answer the questions that were asked.

To my knowledge there is no way to guarantee the same UIDs or GIDs.

and no, the external drive does not need to be modified in any way or reinstalled.

As far as the firmware upgrade, yes Tahoe does include one, but I have no idea whether it needs to be changed or even if it can be when trying to install Sequoia.

elisatems wrote:

So what is the procedure to restore user accounts after the clean reinstall? Do you have to create the user accounts in Users & Groups and THEN restore from TM, or does the TM restore recreate the old accounts transparently?

Assuming you are willing to revert everything and revert all changes and all updates and all of your own changes back to the state that existed prior to the upgrade, and assuming your Time Machine back ups (or whatever other local backups might exist) are deep enough to allow it, you can revert to the old backup, restoring it, and losing all your changes made since then.

If the former, and if there's a mismatch between UIDs / GIDs in the newly created accounts and existing user files, is there a good way to resolve the conflict? A few files under my account are not owned by me or have unusual group ownership, so chown -R does not seem like a good option.

macOS downgrades are not and never have been supported, require a whole lot of work, and require either reverting to the macOS install and manually selecting and transferring individual files, or re-loading a backup from the release and reverting everything that has changed since.

My machine is covered under AppleCare through December of this year. Is this downgrade something that would be covered if I sent it in to Apple?

You’d need to ask Apple that, but I’d doubt it. I’d expect them to install the latest.

There is no general roadmap, no plan, no strategy here, there is only restoring an old backup (probably works), or there is starting over with manual file selection from a newer backup to the restored environment. App files are generally cross-version, but macOS plists and settings, and details from newer versions of the app are not.

Even assuming this all gets stitched together, it may well break again during some future app or macOS upgrade, such as to macOS 27.

1. Because MacOS is (at least under the hood) a Unix system and has UIDs/GIDs, how do I make sure that when I recreate the accounts on my system (of which there are several), they all have the same UIDs/GIDs as currently? Is it possible to specify those parameters when creating a new user immediately after an OS install?

macOS is Darwin, and the Darwin kernel XNU is based on a BSD 4.3 kernel on Mach acquired via NeXT, and with a BSD-ish userland. The many UNIX kernels differ in many ways, and XNU is itself quite unique.

macOS associates GUIDs on many things including users and files, GUIDs which are unique values, and which are generated (uniquely) as needed.

Stitching together an install manually is an immense (read: intractable) effort.

2. There should be no need to restore my personal files from Time Machine, as I will (hopefully) not need to wipe the external drive to reinstall Sequoia. But I will need to restore everything that was placed on the internal disk. Is there a safe way in Time Machine to restore ONLY those files, as opposed to doing a COMPLETE restore of everything in the backup?

Time Machine backs up user files, and does not back up macOS itself. macOS gets reloaded through other means. In this case, through though complete erasure of macOS and erasure of user files, and a new install of the older version. Then manual selection, or restoring an old backup and reverting. And user files contain lots of stuff that gets updated with macOS; settings and preferences.

3. I have seen concerning reports from high-level contributors here that the upgrade to Tahoe involves an (apparently transparent) firmware upgrade. Does that upgrade need to be reversed, and if so, how? (That's an area where I would greatly appreciate a detailed procedure.)

That firmware update stuff has happened in the past, and can block various downgrades.

I don’t know if it has happened with your Mac model somewhere in the macOS 26 range.

TL:DR: I’d skip the downgrade, and would pursue the reported audio issues with Apple support.

You can't re-create the user accountsbecause even if you give them the same names the UIDs, as you note, will be different and then you'll live in a world of access-permission pain for the rest of your days. I believe that the recovery from Time Machine will re-create the correct users/UIDs but I'd wait for a more positive confirmation if I were you since I've never actually done it.

I don't know about AppleCare cos I've never used it, but it would surprise me if it covered free-support for downgrading the OS.

FWIW, a "less dangerous" approach would be to get yourself an external SSD and try installing Sequoia on it. Then just use it for music work only.

This will keep your current system intact and decrease the possibility of totally corrupting and possibly bricking the machine.

In addition, once installed and all is well you can do all the experimentation on that drive before and if you want to commit to restoring the internal to Sequoia.

FWIW, a while back in the early macOS 26 days, I ran into an issue after installing macOS 26 on an M1 MacBook Air, I was totally unable to restore to Sequoia even with using a second Mac to do the restore operation and could only restore macOS 26. So, be warned that a restore may not work.

elisatems wrote:

Addendum: since talking with the rep, I confirmed that if the headphones are connected directly to a USB port (bypassing the hub) the problem did not occur for at least 3 minutes, and given that when going through the hub it always occurs within less than a minute, I tend to think it only happens when going through the hub, so something has changed in the way the OS sees that hub and devices connected to it.

I would suggest using a different hub.

Are you using a cable to connect this hub to the computer? If so, make sure that cable is a high quality cable from a respected brand/manufacturer and the cable is less than one meter in length.

Tahoe tends to need better quality & shorter cables. People with external displays and external drives have found replacing their existing cables resolved their issues. Unfortunately many cables on the market today are just low end types......even cables manufacturers provide with their products will be of lower quality.

elisatems wrote:

*If anyone doubts that there is an underlying problem in the OS, please see the other thread I linked to below last night, and those linked to from that thread. At least one other poster has reported a seemingly identical problem: gradual audio degradation that begins soon after audio starts playing, and that only occurs if the audio device is USB headphones. I have asked Apple to add that link to my case, since the last senior advisor I spoke with said that he had never heard of a similar issue.

I don't doubt that you are experiencing the issue, along with some other users. But have you 100% ruled out the possibility of something installed being the cause? If it is a MacOS bug that certainly won't be the first time such bugs have surfaced ...

I have not experienced this with Tahoe 26.5.1 but my headphones are Bluetooth. Does the audio degradation issue occur with Bluetooth headphones also? I can also connect my headphones through the headphone jack, but the problems reported seem to be with headphones using a USB connection? As a workaround until Apple addresses this, can you connect your headphones via Bluetooth or with a headphone jack?

Availability of a Secondary macOS System is highly Recommend

Confirm that the user ( you ) 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.

weeklycod wrote:

go to App Store search sequoia then install, go to system settings and it will update latest Sequoia and it will restart to Sequoia. it Is made by apple

Technically, downloading an older version of macOS, like macOS 15 Sequoia on a computer that is already running a newer version like macOS 26 Tahoe

We can not just install Sequoia Over the Exiting installation of Tahoe - full stop.

If we may suggest, test this procedure you have outlined, on you own computer before making such a suggestion