Solved.
Nothing to do with Apple Silicon or Julia 1.7.
Bad indexing in MY code.
I plunged ahead and fixed it so no problem. I will reconstruct it to test on 1.6.3. Seems like Julia should have triggered an error for my code and stopped running it, but not crashed. But, I need to look because it involved two layers of indexing. Might abend (there’s an archaic word for you–abnormal end) for 1.6.3 also.
I sort of freak out when I see a segfault and a few dozen lines of impenetrable messages.