"Within the next couple of days, that stopped working, though I could
turn the key and jiggle the shifter into Neutral and back into Park
and then it would work. Then that quit working, so I replaced the
neutral safety switch, to no avail."

That is absolutely diagnostic of bad neutral interlock switch or its
connections, notwithstanding that replacing the switch did not cure it.  If
you can make it crank by jiggling the selector, there is no other
possibility.

That was the problem then.  What is it now?  Maybe same, maybe not.  Only a
meter or test light can tell.

Yrs,
d