All I did was have a tiny little peek at the BIOS settings on the new computer, and something went wonky. It was a little frightening to see the new box rendered unbootable for a little while, right at my bedtime, too.
Fortunately, doing a little reading and playing with it some, I figured out how to clear out that invalid signature stuff.
It was a relief to see the operating system come back on the screen. Whew!

Secure Boot: keeping the computer secure from its legitimate owner, but nobody else, especially not crackers and malware creators.
It makes me think of my company forcing a PIN change every three months on mobile devices then griping at everybody when they get forgotten. I can’t think of the last time I heard of a mobile being cracked by tapping a code on the keyboard. Police, maybe. I assume they have better ways.
Another funny one. All app installs have to be whitelisted by the administrator, which I view as a good idea because employees will install bullshit nilly-willy. I asked for the Google keyboard, Gboard, because the installed Samsung keyboard is horrible. I was told no because it is a security risk. I replied, “the whole damned device is a security risk.” They won’t let me have it.