Rolling Back MacOS on 2020 Intel iMac

[tkitch]

At work, we need to roll back the OS on a couple new iMacs that were purchased.  

 

They're late 2020 Intel i7's 27" iMacs, so they're good machines, but the software requires an older OS to work with some of our servers.  So this isn't an option, it's a requirement.

 

older iMacs were easy to do this to, but these new ones are being difficult.  Has anyone done this and know how to do it?   (I don't usually get stuck supporting the Macs, but today I am.)

Thanks!

[WhitetailAni]

https://support.apple.com/en-us/HT201372

Make a bootable USB of whatever version of macOS you desire, the downloads are on this page. Plug it into the Mac you wish to downgrade, then turn off the Mac. Turn it back on and hold the Option/Alt key on the keyboard, you'll get a boot menu.

Select the "Install macOS insertOSnamehere" drive, and install!

[BondiBlue]

What version of macOS do you need to run? macOS Catalina is the oldest version of macOS that those machines ever supported, so if you need to run anything earlier (Mojave, High Sierra, etc.) you're out of luck. You can't just install whatever version you want. 

 

If you need to run a version of macOS older than Catalina you can try using Parallels Desktop or VMware Fusion to run the older version in a virtual machine. Neither are perfect solutions, but that's the best you'd be able to do on a newer machine. 

50 minutes ago, FakeKGB said:

Make a bootable USB of whatever version of macOS you desire, the downloads are on this page.

See above for more information, but you can't just install whatever version you'd like. The 2020 27" iMac only supports Catalina, Big Sur, Monterey, and (later this year) Ventura as of right now. No older versions are going to run natively on it. 

[tkitch]

1 hour ago, BondiBlue said:

What version of macOS do you need to run? macOS Catalina is the oldest version of macOS that those machines ever supported, so if you need to run anything earlier (Mojave, High Sierra, etc.) you're out of luck. You can't just install whatever version you want. 

 

If you need to run a version of macOS older than Catalina you can try using Parallels Desktop or VMware Fusion to run the older version in a virtual machine. Neither are perfect solutions, but that's the best you'd be able to do on a newer machine. 

See above for more information, but you can't just install whatever version you'd like. The 2020 27" iMac only supports Catalina, Big Sur, Monterey, and (later this year) Ventura as of right now. No older versions are going to run natively on it. 

Well, that's gonna make life difficult, since we do need Mojave.....  

[SydneyBrokeIt]

Your best (likely only option) will be to virtualize Mojave.

 

If I can ask, what software is this, and can you cajole the vendor into support something newer?

[FUIT1985]

macOS Recovery installs different versions of macOS (On an Intel-based Mac) 

 

Shift-Option-Cmd-R

 

during startup to get the version of macOS that came with your Mac or the closest available version to it.

 

https://support.apple.com/kb/HT204904

[WhitetailAni]

On 6/10/2022 at 12:04 PM, tkitch said:

Well, that's gonna make life difficult, since we do need Mojave.....  

You might be able to do some funky stuff with OpenCore, but I don't recommend it for a production environment.

[BondiBlue]

1 hour ago, FakeKGB said:

You might be able to do some funky stuff with OpenCore, but I don't recommend it for a production environment.

I haven't looked into it, but I'm not sure that would work, and even if it did it's not something that should be used in a production environment like you mentioned. VMware Fusion or Parallels Desktop are the only two options for OP outside of buying an older iMac that supports Mojave. 

[Roswell]

On 6/11/2022 at 1:26 AM, SydneyBrokeIt said:

Your best (likely only option) will be to virtualize Mojave.

 

If I can ask, what software is this, and can you cajole the vendor into support something newer?

Sounds like it’s a 32 bit application since Mojave was the last to support them.

[tkitch]

On 6/11/2022 at 1:26 AM, SydneyBrokeIt said:

Your best (likely only option) will be to virtualize Mojave.

 

If I can ask, what software is this, and can you cajole the vendor into support something newer?

they're working on it, but that doesn't help now.  

 

Vendors are slow, so I'd be an optimist to say 'this year'

[DrMacintosh]

On 6/10/2022 at 7:36 AM, tkitch said:

They're late 2020 Intel i7's 27" iMacs, so they're good machines, but the software requires an older OS to work with some of our servers.  So this isn't an option, it's a requirement.

It’s impossible to use a version of macOS prior to the version that shipped with the Mac, so macOS Big Sur, which was the 2020 release of macOS. If your program won’t run on Big Sur, then it won’t run on those Macs at all and you’ll have to find different computers. Catalina might be possible but it’s not old enough to get the application support you need.