How to install macOS Sierra 10.12.6 on a newer Mac for Final Cut Pro 7 compatibility?

John Galt wrote:

You will need to erase the Mac first.

Since you have Sierra already running on similar Macs, you can use one of them to create a "bootable USB installer" with the following instructions:

Create a bootable installer for macOS - Apple Support

Briefly stated, using one of those Macs, download the "full macOS installer" for Sierra as it describes. Once it is downloaded with the installer app residing in the Mac's Applications folder, and the USB flash drive connected to the Mac, copy the appropriate command and paste it into a Terminal window. You will notice there is no specific command for Sierra, however, I am not aware of any app that runs under Sierra that will not run under High Sierra. Your other Macs ought to be able to update to it as well, with no disadvantages. So, although you seek to install Sierra it's my recommendation that you install HS instead.

Unfortunately the macOS 10.12 Sierra installer has been broken in respect to creating a bootable USB installer for many years now (since at least 2021). Some of us notified Apple with feedback & even in The Lounge, but Apple decided to remove those instructions rather than fix the Sierra installer. Notice you can download the Sierra DMG installer, but Apple does not have the command line instructions for Sierra.

It is very easy to fix the Sierra installer by following the instructions in the following post which modifies the version number within the Sierra installer located in the Applications folder (requires using the command line). See the post by Eau Rouge from 2021 (I have some as well):

Trouble creating bootable disk for Sierra -- @Eau Roughe's Fix - Apple Community

They even include the proper Terminal command that is missing from Apple's instructions for creating a bootable USB Sierra installer.

Amazing a trillion dollar company is unable to provide such a simple fix themselves and instead hides away the instructions for Sierra to eliminate the problem.

olivertom1 wrote:

Thank you very much for taking the time to find these things and replying with a clear explanation. In trying to figure this out over the weekend, I'd gotten all the way to trying to create a bootable disk with Sierra on it. But the point you make about no command for Sierra is the problem I ran into: I just could not create a command in Terminal that would work. I tried both the described "macOS" format for High Sierra and the "OS/ X/" command for El Capitan. Neither would complete the process and make a bootable disk. As for all the applications working under High Sierra, that is certainly a logical deduction, but actually there is one: the best full-feature video editing program Apple ever released, Final Cut Pro 7. But some changes they made in the High Sierra upgrade rendered it unable to run FCP7. I guess that's because the High Sierra upgrade was simultaneous with the decision to discontinue the original Final Cut Pro updates, smarten up iMovie a bit, and call it FCP X for the expanding consumer market. But X is nothing like FCP7 in terms of compositing and other complex edit stuff. Which is why I still run FCP7. On the other hand, FCP7 does run on El Capitan, so I'll see if I can get El Capitan to load. Again, thanks so much for helping on this. /tom

What you could do - assuming the "newer Mac" is an Intel Mac - is install OS 10.12 in a virtual machine (e.g. Parallels, VMWare, or VirtualBox) which you can then run alongside the newer OS. It helps if you have good RAM - e.g. 16GB - as you will be running two OS's at the same time.

You will need to erase the Mac first.

Since you have Sierra already running on similar Macs, you can use one of them to create a "bootable USB installer" with the following instructions:

Create a bootable installer for macOS - Apple Support

Briefly stated, using one of those Macs, download the "full macOS installer" for Sierra as it describes. Once it is downloaded with the installer app residing in the Mac's Applications folder, and the USB flash drive connected to the Mac, copy the appropriate command and paste it into a Terminal window. You will notice there is no specific command for Sierra, however, I am not aware of any app that runs under Sierra that will not run under High Sierra. Your other Macs ought to be able to update to it as well, with no disadvantages. So, although you seek to install Sierra it's my recommendation that you install HS instead.

Apple has not sold any refurbished Macs capable of running OS X 10.12.6 "Sierra" for a very, very long time. So, you will need to explain what you have, how you obtained, it, are you in possession of its original installation media... etc.

Writing an effective Apple Support Communities question - Apple Community may help you to obtain the necessary details.

olivertom1 wrote:

(I'm running Sierra on three similar machines, but I need a backup for one of them, and I've never had this problem before.)

Have you thought about using one of them to prepare an external startup drive containing Sierra, or High Sierra, to be used as an external startup drive on the new machine?

There are no specific instructions for Sierra, hence my recommendation.