Mac Mini kernel panic loop

[hilarity n. suze]

My husband uses a Mac. Mojave OS. He downloaded (or uploaded?)* an update and now his computer keeps turning itself off with a black screen of death, which I understand is similar to a blue screen of death of my computer and is a very bad thing.

We have searched the internet for a fix, and there are lots of weird things to do with a Mac, like turn it on and hold the R and control key (?). Nothing has worked. I told him to look for a restore point, but I don't know if Macs have restore points. Anyhow it keeps turning off...

I hope he doesn't need a new computer...Does he?

Any help appreciate, TIA.

*He is not sure what he did. Something said "Okay to update?" and he said, "Yes."

[Pencil]

Black screen of Death?
Does it show a folder with a question mark?

If so, you need to reinstall the OS. IME it won't work with WiFi, so connect an ethernet cable.
Boot the computer holding down cmd+r. If you get a spinning globe, follow instructions to re-download the OS.

If you google Mac OS folder question mark you'll get loads of pages offering other solutions, should this not help.