Still trying to down-install 10.12 Sierra to my 2015 machine after lots of steps taken

Question

Level 1

4 points

Still trying to down-install 10.12 Sierra to my 2015 machine after lots of steps taken

Still trying to get OSX 10.12 to install on my 2015 computer so I can run Final Cut Pro 7. I've tried to execute the suggestions for creating a bootable disk (since Apple failed to set this up for Sierra), so I finally thought I'd try install ing El Capitan, then upgrade that. But the copy of El Capitan I got when I went to Apple's page for earlier operating systems came back as "damaged" when I tried Recovery on the 2015 Mac running Monterrey. The whole thing worked in Recovery as it should, then as it was seeming to finalize, the gave me this "damaged" message, and to restart. All the restarts got to the same place. Downloaded the OS again, made a new bootable disk with a new thumb drive. Same result. ANY HELP or thoughts on this frustrating dilemma..???

And when I used the suggested prompts for creating the Sierra disk directly, every time it came back as "not a valid mount point," whether I used MyVolume or changed it to "Sierraboot" or something else. I must be doing something wrong, but I have no idea what it could be.

Earlier Mac models

Posted on Dec 26, 2025 9:16 AM

Reply

Answer 1

HWTech

Level 9

68,828 points

Dec 26, 2025 10:17 AM in response to olivertom1

olivertom1 wrote:

And when I used the suggested prompts for creating the Sierra disk directly, every time it came back as "not a valid mount point," whether I used MyVolume or changed it to "Sierraboot" or something else. I must be doing something wrong, but I have no idea what it could be.

You need to first fix the broken Sierra installer by using the command line to modifying the installer before you attempt to create the bootable USB installer. See the following post by @Eau Rogue:

https://discussions.apple.com/thread/253126563?answerId=255858666022&sortBy=oldest_first#255858666022

Unfortunately Apple has made a complete mess of these older installers and is not properly fixing them or providing a simpler method for downloading & creating bootable USB installers. In fact over 4 years ago Apple removed the command for creating a Sierra USB installer instead of actually fixing the broken installer. It has only gotten worse since then.

If you don't have access to another Mac compatible with Sierra, then you should first install macOS 12.x Monterey using Internet Recovery Mode (Command + Option + R). You can then create a bootable macOS 10.12 Sierra installer & perform another clean install of macOS...this time for Sierra.

Reply