Downgrade macOS from Monterey to Catalina on 2014 Mac Mini with external disk

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Downgrade macOS from Monterey to Catalina on 2014 Mac Mini with external disk

I need to run Catalina on my Late 2014 Mac Mini, which originally came with a much older macOS. It is currently booting from an external SSD into Monterey because the internal HDD is so abysmally slow.

I have another SSD attached which is APFS formatted and has a number of partitions, one with Monterey on it and one with Big Sur. There is another partition which has been erased and is ready for Catalina.

How do I get it onto there?

I have downloaded macOS Catalina and have 'Instal macOS Catalina' in the app folder. I have created a bootable installer from it to a USB disk. When I press Option during restart, the bootable installer never appears as an option, just 3 of the other disks attached.

I have tried Cmd-Shift-Option-R but the second option isn't 'Reinstall macOS' which might get back to the original OS that was there in 2014, its always 'Reinstall macOS Monterey'.

Trying to run the 'Install macOS Catalina' from the App folder fails as well.

I tried going to How to get old versions of macOS - Apple Support 'How to get old versions of macOS' where the first paragraph says " ... you might be able to upgrade to an earlier macOS, such as macOS Big Sur, Catalina, ...", and this is where I managed to download Catalina.

I did boot to one of my other disks which is running macOS Big Sur, but trying to run 'Install macOS Catalina' says 'This copy of the macOS Catalina installer application is too old to be opened on this version of macOS.'

Any suggestions??

Mac mini, macOS 12.5

Posted on Aug 17, 2022 1:48 PM

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Answer 1

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PRP_53

Level 10

92,497 points

Aug 18, 2022 3:31 AM in response to AndrewCSP

This will be problematic, somewhere is Catalina, attempting to boot from an External Drive with several other USB Drives connected even using the Option Key will not work.

This is from Observations on these Forums.

A more sure way would to have Only One Drive ( Exception the multi Partitioned Drive with various Versions of macOS Installed ) this would count as Muti USB Drives

The Operations System is looking and looking for the Startup Disk and us confused resulting in the USB Installer Drive not working as in Booting into it.

My suggestion is to get another New and Spectate Drive with Only One Partition and attempt to boot the computer with Only The USB Installer attached. Once don, connect the New Drive and point the Installer to that drive

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