Downgrading macOS without backup

DatBoiCoding Said:

"Downgrading macOS without backup: Hello! I have quite a situation, recently I updated my MacBook Pro 2012 to Catalina, after updating I realized that my 32 bit apps wouldn’t work.[...] but that backup was make a while ago and it was a different file type so I would guess it isn’t compatible because the update was from I think 10.11."

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You would Manual Reinstall:

Create a Time Machine Backup. From there, fully delete the partition. From, install macOS X 10.12 Sierra. From there, migrate it all back. - Use a USB Bootable Installer to create It.

A. Create a Time Machine First...

Create a Time Machine Backup of your Mac, that way you can have something to restore your Mac from, should anything go wrong with the install, and to migrate it all back. Use an External Hard Drive at least 1.5 times the size of the Internal Hard Drive.

B. Then... Reinstall the Mac OS that was Previously Installed.

I. Create a USB Bootable Installer:

1. Go Here: How to Create a Bootable Installer for macOS - Apple Support
2. Use: The in Terminal In Catalina to create this for macOS X 10.12 Sierra

II. Erase the Hard Drive:

1. Boot: into Recovery Mode: Hold Down [Command + R] upon boot
2. Select: Disk Utility
3. Erase: the all partitions

III. Boot From USB Bootable Installer:

1. Plug in: the High Sierra USB Bootable Installer
2. Hold Down: Option upon Boot
3. Proceed: from there as necessary with the Install

C. Once Installed...

I. Create a Second Time Machine First...

Create a Time Machine Backup of your Mac, that way you can have something to restore your Mac from, should anything go wrong with the install, and to migrate it all back. Use a Second External Hard Drive at least 1.5 times the size of the InternalHard Drive.

II. Use Migration Assistant:

1. Go Here: How to move your content to a new Mac - Apple Support
2. Scroll to: Use Migration Assistant
3. Proceed from there as necessary

III. Reinstall Manually

1. Contact: the Developer for the license
2. Update: the System Software (except for the macOS)
3. Proceed from there as necessary

your biggest problem is photos which Catalina will have converted.

Before downgrading and whilst in Catalina export all your photos and on the export options choose either originals, or if you want to keep the edits export the images at maximum size and quality. The resulting .jpgs can be reimported into the Sierra photos app.

(Good idea to export jpgs every so often as a backup anyway).

Select all photos then File, Export.

If you want to keep Catalina or go back to Sierra upgrade Hard Disk to SSD. My 2012 mbp with 16GB ram and SSD is very fast. Youre looking at around $£€100 for 500GB SSD

You could.

Depending on where your files are that you want to keep, only these, move them to iCloud.

Now, download the Mojave installer to a USB, erase Macintosh HD, and click either Reinstall macOS or Install macOS.

Fill in the details. Once the setup has finished, download your important files from iCloud. Move them to where they were.

Remember, only the files you need. It is not possible to downgrade and keep data without some trace of a backup.

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JavaSight

[Link Edited by Moderator]

DatBoiCoding Said:

"We have tried to downgrade the Mac already to 10.15-10.13.6 but after installing the new software we went to use the migration assistant but it said that the backup could only be used on 10.15."

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Re-upgrade, then Re-downgrade:

If you never backed up this macOS X 10.12 Sierra machine (which I mistook it that you did), then it wouldn't transfer over. That is because of the format. This APFS Drive is incompatible with macOS Extended(Journalized), which is why it is not reading.

So...

Are there are any files you are concerned with losing? If not, just contact the developers of the applications you had installed, asking them for a reinstallation file and key.

For Thought:

If you are uncertain of what software they are, then you need to re-upgrade, using the Time Machine I recommended in my above reply. From there, take a picture of the applications with your phone, and transfer files a folder to iCloud or to a flash drive.

Before Re-formating to APFS:

Contact the developers, asking them for a compatible installation file. Once all is retrieved, downgrade again, and install these application via a 32Bit or 64Bit installation Software File - whichever pertains to your Mac. And then transfer these files and folders over from the Flash Drive.

Well I don't fiddle about with backup drives, they are too delicate, I'd rather find or buy another drive, but if you know how then go ahead.

What about the converted photos library?