Downgrading from Mojave to High Sierra ... lessons learned

[derekw]

Originally Posted by dnanian

There's definitely nothing in that article that would suggest a special terminal command is necessary to recognize an external device at Option+Power On... I'm quite familiar with everything in there. Would really like to understand what, exactly, they asked you to do, since it's totally news to me.

I called Apple again but they can't find the command line they sent me yesterday. Meanwhile, I found this Apple support article about choosing startup disk which includes some command lines. I don't know if that's what I did though. https://support.apple.com/en-ca/HT202796

Extra info: There is a Option-Shift-Command-Period method mentioned in the article. I also tried that but it didn't work. I was using an Apple wireless keyboard so I don't know how reliable it is on these startup actions. The drive was not encrypted (no FileVault) and no firmware password was set.