Downgrading to Big Sur
I've got 5 macs here, all on Monterey. There is one machine, a Mac Mini 2018 which I would like to downgrade to Big Sur (I'll spare you why). The issue is that no matter what I do, this machine will not allow me to do the downgrade. Data on the drive is completely expendable so I've formatted it. It's got nothing now. Here's what I've tried.
- I downloaded Big Sur from the Apple Store onto my 2019 iMac (a few days ago, before the Mac App Store was having difficulties).
- I followed the instructions to make a bootable USB drive.
- I go to the Mini and hold option, boot into the image from the USB drive, when I click "Install Big Sur", it comes back with the big sur installer is damaged.
Online searches say something about an expired certificate which makes zero sense because I literally just downloaded the thing. But anyway, I used the softwareupdate terminal command to retrieve a fresh copy, rebuild the usb drive, same thing.
Then I tried a different USB drive. Same thing.
Then I re-downloaded (third time) the image using installinstallmacos.py. Same thing.
I checked if my clock was off (terminal: date). Nope, it's correct.
Then I booted into Internet Recovery thinking since the machine shipped with Mojave, it might present that as an option. Nope. It wants to install Monterey.
I also tried just launching the install Big Sur app to install onto a different SSD drive and it won't launch from Monterey, but I have no macs that aren't Monterey now.
I'm completely bald but if I had hair, I'd pull it all out. I've been working on this all day. The simplest task of installing an operating system one level back on a fresh disk is seemingly impossible yet online guide after online guide seem to make it seem easy - even Apple's support docs make it sound possible.
I think if I could get past the "installer is damaged" error, it would work. Is that happening because it's reaching out to Apple and Apple is having issues right now? That's all I can think of. I'm out of ideas.
Mac mini, macOS 12.0