As it were, the cable that I took to my neighbor's home was not used.

FWIW, I was careful to carry the cable in a clean bag so the pins don't corrupt (my common practice).

I have also tried restarting from a cold boot. Again, no joy.

Harv
27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire