Downgrade to older macOS


I got a little too adventurous a month ago and used the generally excellent OpenCore Legacy Patcher (OCLP) to upgrade a 13" mid-2012 MacBook Pro directly from Catalina to Sonoma. I had been using this machine for most of my casual, personal browsing. It also has a 4TB internal SSD, so it is very useful for many storage-related tasks.

I know upgrading to the unsupported Sonoma was risky, but I had a backup, and others had successfully performed similarly complex OCLP upgrades, albeit on different hardware, so I decided to take the risk.

At first, I was very happy with the system on Sonoma once I updated various apps and tweaked a few settings, though I would experience crashes in Safari and the Music app after a few days of heavy use. Unfortunately, over the last couple of days, Safari and Music started crashing so frequently that machine really is no longer usable for what I want to do. (FWIW, it’s only Apple software that seems unreliable on this system. Aside from issues with virtualization software, a well-known issue in certain OCLP configurations, third-party software generally has been fine.)

With that as background, the pros, cons, and risks of OCLP aren’t really what I am interested in discussing right now. (I’m happy to discuss OCLP in a different thread if others are interested.)

Downgrading to Catalina

I’m interested in any tips the community might have for moving the system back to Catalina as efficiently as possible while retaining access to any files I’ve created since my last pre-OCLP Catalina backup.

Yes, I’ve done my homework and read a few articles on downgrading macOS, including some here at TidBITS.

Here is an outline what I am planning to do:

  1. Back up the OCLP Mac to an external drive.
  2. Use another machine to create a bootable USB Catalina installer.
  3. Boot the OCLP Mac from the Catalina USB installer.
  4. Do a complete “nuke and pave” installation by completely erasing the 4TB drive before running the installer.
  5. Use Apple’s Migration Assistant to restore users, apps, docs, and settings from my last backup of the original system taken when it was still running Catalina.
  6. Attach the OCLP backup and use Ted Tempelmann’s excellent “Find Any File” to track down documents on the OCLP that are new or modified since my ill-fated Sonoma adventure and then copy those over to the Catalina system.

Am I missing anything? Any tricks to make the process faster or more efficient, especially step 6, which I presume is the most labor-intensive of the steps?

Thanks in advance for your comments!


You said you have a Catalina backup so couldn’t you use that to reinstall your Catalina volume? I’ve used Carbon Cloner Copy to make bootable backups of my Catalina volumes with no issue but later OS’s are different I know. You should be able to boot from your backup and just use CCC to clone. As for your data files from the OCLP upgrade, you should be able to copy those from your account. The Find Any File method should also work as a backup plan.

I also upgraded my 2012 Mac Mini to Sonoma and it has been fine so far but I don’t use it daily so I can’t say it won’t experience issues but others on the MacForums site that have similar equipment are also reporting success with Mini’s. I don’t know if you follow that thread but here it is and maybe there’s something else you can do to fix your problem before going back to Catalina:

One other thing since you mentioned you have a 4TB drive: you could add another volume and reinstall Catalina there and keep the Sonoma one for future possible use once you figure out if it can run properly.

Where are the new files located? Are they in your Documents folder or scattered elsewhere like Library and its subfolders? I would be tempted to use Carbon Copy Cloner or a folder compare/sync utility and point it at specific folders.

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