New development. I didn't have a crash in a few days, so I was hoping that the problem was solved, but now it happened again (yesterday and today), and when the computer restarted I came to the BIOS screen (see pic). If I read that screen correctly (can you verify?), it says I have no M2 SSD drive (the system drive), so a likely cause seems to be intermittent failure of the SSD device. After turning off the computer, letting it rest for a minute, it starts again.
Running the Corsair Diagnostics doesn't reveal any errors.
So I guess I should buy a new M2 drive. Any other advice? Like, opening the computer and check the SATA cable or whatever?