One thing people don't generally know is that as developed in Japan it's a quality control system. If a jig at a supplier gets out of alignment and parts made with it are out of spec and not noticed until assembly, you're better off with a feedback loop measured in hours instead of months.
COVID and the silicon shortage ... I'm not even sure JIT has any relevance, one of the biggest problems in the US was car makers canceling orders when as you could easily predict from historical plague patterns the demand for cars would go up as people left cities. Demand for a whole bunch of things changed due to the secular changes in the economy like work from home, JIT's shorter feedback loop might even help with that.
But chips are indeed one thing that shouldn't be done in JIT style. They inherently take a long time to make and are relatively easy to test. Toyoda was said to have changed their inventory strategy for them after the disruptions of the earthquake and tsunami.
And then there are disruptions like a fire taking out a fab line, I remember this happening in Japan for embedded type chips. Unlikely any relevant inventory policy would save you from that especially if there's an increase in demand where stockpiling won't save you.
The industry can't even in theory surge old nodes for which the equipment is no longer manufactured. We hear a not uncommon pattern is that they'll just suddenly stop making chips forever because they can no longer fix a critical machine.
