Downgrading caveat, and a detailed guide

[Fowl]

I have recently found this:

How to Downgrade from macOS Tahoe to Sequoia: Complete Guide with Data Safety 2025

Step-by-step guide to safely downgrade from macOS Tahoe 26 to Sequoia 15. Protect your data, avoid common pitfalls, and restore your Mac's performance with three proven methods including Time Machine, bootable USB, and Internet Recovery.

macos-tahoe.com

This is the most detailed guide for downgrading from Tahoe I have seen, with much information I have not seen elsewhere.

If I knew two weeks ago what I know now, I wouldn't have upgraded to Tahoe. If I had read this guide, I wouldn't have bothered downgrading to Sequoia, because:
Mail and Photos are not backwards compatible. When you upgrade to Tahoe, the databases for both programs get upgraded to a new format, which Sequoia can't read. When you downgrade to Sequoia, your mail and photos will then be unreadable.
If you use IMAP, you can resync your mail. If you export your mail and photos to some neutral format while in Tahoe and then reimport them under Sequoia (which is hard and incomplete), you can sort of get around this problem. Since I didn't know about this, I had to upgrade to Tahoe yet again.

 

[TumbleDryer]

Mail and Photos are always like that. I think Apple do it on purpose. I'd personally manually save all my photos, music and movie files into a folder and treat them like any other type of file then manually add them back in building up albums and playlists again from scratch. PITA but that's Apple for you.

WIth IMAP mail as you say just add in your account details and everything should just repopulate as it's all saved on the server and Mail app just reads it from there. If you have moved emails from the Inbox to other folders however make sure those folders are on the server and have not been created locally as you will lose them if they are local. You would then treat these local emails/folders like the above images and movies etc. Normal files, stick them in a folder a re add them later.

EDIT: Just had a quick read and its a very good guide and covers what I said above.

 

[Apple Knowledge Navigator]

The two things keeping me on Tahoe are the improved Shortcuts functionality and the Control Centre (the combination of both having replaced many of my old menu bar items). If I still had a Mac as a home server, I would probably downgrade.

I think Tahoe has a lot of good features, but it's just so frustrating that these are spoiled by bugs and a ridiculous UI. I really don't like the defence of "Yeah, but Apple will refine it over time". What absolute nonsense. Apple set its own 12 month release cycle and they should hire/manage to that accordingly.

I'd honestly rather them just announce new features incrementally over .1 releases, for at least that would become available once they're actually ready. The whole annual push for a new 'big' release appears more a marketing strategy than a productive one.

 

[Fowl]

This was the first time I tried to downgrade a system, because it is so buggy. I seriously wonder if there was some upheaval in the software division, like key people leaving or bad managers being put in key positions. I'm sure the rank and file at Apple realize how bad it is.

 

[Mike Boreham]

Three ways round the Photos library problem:

1. If you are using iCloud Photos delete the Tahoe library, create a new one, turn on iCloud Photos. It will re-download all your photos into a new Sequoia library.

2. Repair the Tahoe library using the Apple Library repair tool. This little known and undocumented way works, from personal experience, on an iCloud library. But I haven’t personally used it on a non-iCloud library. I also haven’t used it on a Tahoe to Sequoia change but it worked previous two macOSes.

3. Save a backup of your Sequoia Photos library before updating to Tahoe and use it when you downgrade.

All three, even the last, will take some time depending on size of library.

Method 3 is best if you can do it. Then Method 1, and method 2 as last resort.

 

[TaylorA]

Three ways round the Photos library problem:

1. If you are using iCloud Photos delete the Tahoe library, create a new one, turn on iCloud Photos. It will re-download all your photos into a new Sequoia library.

2. Repair the Tahoe library using the Apple Library repair tool. This little known and undocumented way works, from personal experience, on an iCloud library. But I haven’t personally used it on a non-iCloud library. I also haven’t used it on a Tahoe to Sequoia change but it worked previous two macOSes.

3. Save a backup of your Sequoia Photos library before updating to Tahoe and use it when you downgrade.

All three, even the last, will take some time depending on size of library.

Method 3 is best if you can do it. Then Method 1, and method 2 as last resort.

Just downgraded from Tahoe to Sequoia yesterday and lost access to Photos and Mail. #2 worked perfectly to restore my Photos Library and I can't thank you enough.

 

[bzgnyc2]

I have recently found this:

How to Downgrade from macOS Tahoe to Sequoia: Complete Guide with Data Safety 2025

Step-by-step guide to safely downgrade from macOS Tahoe 26 to Sequoia 15. Protect your data, avoid common pitfalls, and restore your Mac's performance with three proven methods including Time Machine, bootable USB, and Internet Recovery.

macos-tahoe.com

This is the most detailed guide for downgrading from Tahoe I have seen, with much information I have not seen elsewhere.

If I knew two weeks ago what I know now, I wouldn't have upgraded to Tahoe. If I had read this guide, I wouldn't have bothered downgrading to Sequoia, because:
Mail and Photos are not backwards compatible. When you upgrade to Tahoe, the databases for both programs get upgraded to a new format, which Sequoia can't read. When you downgrade to Sequoia, your mail and photos will then be unreadable.

Yes this is an unfortunate result of Apple's unrelenting "tweaking" of the on-disk format/structure/etc for Mail, Photos, Music, etc between major OS versions. Which of course are every year. If you look in the ~/Library/Mail you will see that they version the format for any current OS. Mojave was V6, Catalina was V7, Monterey V9, and Sonoma was V10 (I assume Big Sur was V8). Not sure why Apple needs to change the on-disk structure for Mail -- a program that's been pretty solid since ~ MacOS X 10.1 -- every year for the past 8 years. Also not sure why Sequoia also versions its database V10 but is incompatible with Sonoma...

Sonoma also doesn't like Sequoia's on-disk structure for Music. Okay maybe an incompatible change was necessary with Big Sur's shift from iTunes to Music, but again seemingly every version? I thought that was the point of these XML/plist formats was not everything needs to be incompatible all the time.

If you use IMAP, you can resync your mail. If you export your mail and photos to some neutral format while in Tahoe and then reimport them under Sequoia (which is hard and incomplete), you can sort of get around this problem. Since I didn't know about this, I had to upgrade to Tahoe yet again.

Yes IMAP solves the problem on the mail side if you don't have local folders. Otherwise conversion is usually possible but may be time consuming. One approach that usually works even after the fact is to use IMAP as the hub -- move all your local mail to an IMAP server in Mail, downgrade, move it all back under the newly installed old OS's Mail. Depending that could require a lot of time and IMAP server capacity.

Presumably something similar is possible with cloud-based options for Photos but not something I've tried.

Not sure the alternatives for Music.

To me these are all good reasons to slow down the OS releases, decouple the iLife/etc apps from the OS, and minimize breaking changes in the app databases, but Apple is the multi-trillion dollar company out of the two of us...

 

[Ben J.]

Just so people know; Downgrading from Tahoe to Sequoia is a perfectly non-destructive process as long as you, after installing Sequoia from a bootable installer, restore from a backup that was created while still on Sequoia.

 

[TaylorA]

How many of us realistically knew Tahoe was going to be such a mess before upgrading from Sequoia? Do we need to just keep bootable installers of every OS on hand just in case Apple's newest (basically forced) upgrade is a complete failure as I believe Tahoe is? Although some of the components don't function as they did on Sequoia I'm happy to have my battery life back before Tahoe destroys it completely. After over 30 years I have lost my trust in Apple's ability to design truly functional software that doesn't include a bunch of fluff like Liquid Glass. Who could have predicted this and taken preemptive steps to prepare for it?

 

[Fishrrman]

Taylor moans:
"How many of us realistically knew Tahoe was going to be such a mess before upgrading from Sequoia? Do we need to just keep bootable installers of every OS on hand just in case Apple's newest (basically forced) upgrade is a complete failure as I believe Tahoe is?"

Ummmm....
There's a very EASY way to discover such things, and know what's going to happen BEFORE you "upgrade" your internal SSD. I'm going to give you some of the best advice you're ever going to get:

First, get an EXTERNAL USB3 or [better] USB3.1 gen2 (also called USB3.2) SSD.
Either buy one ready to use, or put one together yourself.

Next, install the new OS (or developer/beta version, if you wish) onto the EXTERNAL SSD.

When the install is done, either set it up as a "new" drive, or migrate some or all of your apps and stuff over onto it -- without affecting your internal boot drive and old OS.

You'll now have a way to boot up and "test run" the new OS and see how it looks and how your apps will interact with it.

The external SSD won't be quite as fast as the internal, but once booted, it will be "pretty close".

If you encounter problems, then don't install it as your "main OS" (on the internal SSD) yet. Just "boot back over" to the internal drive and use that, as well.

I've been doing this for years now.
Works great.

 

[losthismarbles]

For me it was the 26-introduced Phone App..
Literally the only reason (after it went live) i bought an iphone.

When, while planning it, i remembered i couldn't have that going back to Sequoia? Yeap, end of story; unfortunately 🙂

Now --off topic-- the irony is if you know what you're doing, you can as i've only recently found out have the "Phone App" equivalent from your custom ROM Android phone. I don't mean what Apple selectively allows Google to port/implement on Android, i mean literally the whole nine yards, open sourced.
Meaning, i could have had my second, mobile setup (one in my sig) with ANY, any non-Apple laptop of my choosing made to be running PoP OS + Cosmic and with any Android mobile.. even a potato one.
Waste of money therefore, but, live and learn 🙂

At the very least, i can now say, due diligence put in and facts accumulated, why i'm really not an Apple person, never tried their vaunted "ecosystem" before. Knowledge worth paying for. How would you know ^^