I bought a refurbished 2015 MacBook so that I could continue using my legacy software, but its SSD came preinstalled with OS 10.14 Monterey. I want to degrade it to 10.12 Sierra. I have a Time Machine / bootable external HD but can't work out how to erase the new SSD and put Sierra on it. I've tried everything, including creating a HFS partition on the SSD, but when I try to run disk utility from the external drive, it doesn't even see the SSD.
WHAT HAS BEEN TRIED:
(This video seems to address the problem via BIOS settings but I can't work out how to get to the BIOS that he shows on the screen -
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WHAT HAS BEEN TRIED:
- Booted in recovery mode - doesn't help, cannot restore Sierra onto the SSD.
- Booted from Sierra Time Machine backup external drive.
- Booted from a dedicated external Sierra boot drive.
- In all of the above, have tried "Restore", "Install New OS", and "Disk Utility"; in these attempts, the SSD drive doesn't appear as an option.
- I have tried within Monterey, partitioning the new SSD, creating a HFS partition in order to install Sierra on that. This generates error messages that appear to be some kind of incompatibility between Sierra and Monterey. EG, "Error 13" which appears to be some kind of Unix code.
- Or when I choose "Restore" to the new partition, I get the error, "Source volume format on device is not valid for restoring"
(This video seems to address the problem via BIOS settings but I can't work out how to get to the BIOS that he shows on the screen -