> Does every car mechanic need to be able to explain the principles of a combustion engine?

Probably. I’d certainly not want to use a mechanic who doesn’t understand the combustion engine, or who is incapable of giving at least a high-level overview of it.

Not sure that's right in general. Steam trains -> electric trains, ICE cars -> electric cars, thermionic valves -> transistors, copper wire -> optical fibre, incandescent bulbs -> LEDs, CRT televisions -> digital televisions, film cameras -> digital cameras. Same sort of thing with more efficient technology.

For software, we've gone from machine code to high level languages, but were still writing algorithms, which is the important thing as you still use your brain for that. Until vibe coding came along.