I clobbered my dual-boot laptop. I ought to have clobbered it long ago, so it was uni-boot Linux, but that whole secure-boot UEFI firmware business scared me too much to do that without knowing more, and who has time to learn more, or a test-bed on which to make mistakes.
I was running Ubuntu 17.10 for awhile, but [I made, over a period of two months, a long list of trivial changes that made me decide the simplest thing would be if] I decided to reinstall the OS. And that didn’t work. Or, it sorta kinda worked once or twice, then quit working completely.
Did I run into the Ubuntu BIOS bug? I don’t know. But I was installing Ubuntu and I couldn’t get past the BIOS. So maybe I did. But I don’t know.