Microprocessors are always the choke point, where I’d be hard pressed to reproduce one, and they form the basis for so much else.
What about a bunch of other things like smelting iron or teaching everyone to read? They don't seem like choke points because we are long past them.
Producing cheap iron is hard.
Producing even the simplest IC? Definitely not. And that is ignoring the need for electricity and everything else required to actually use it.
Even going to 1925 and teaching how to make a MOSFET would help.
Not particularly micro, but a processor nonetheless.
If the drinking water is far away at the top of a mountain it isn't so convenient to throw your garbage in it, take a dump in it or float the dead in it.
(a TTL 4004 would be an energy drain and would be hot, but it would work). I think CRAY used ECL