Would calling Apple on an out-of-warranty machine do anything? I do have another Mac with a warranty, so I could immitate that that's the machine that has the issue, if need be.
Not sure doing so will help. Once you get so far into a technical situation like this, they’d want to look at the machine, and you’d be busted. I can’t recall if you mentioned it, but have you tried resetting the NVRAM?
https://support.apple.com/en-us/HT204063