Yeah as long as you ignore the engine (ECU/PCM/TCUs) in cars in the 80s, they're quite simple. Go back to the early 70s-before and it's mostly all analog or trivial electronics.
Alec of Technology Connections just posted a video on this:
This and the video on hybrids, are, imo important works, because they break things down in a way that disarms tribalism, and explain how it is that we got to where we are. There are very real stakes in ownership, right to repair, and freedom of movement that rest on people having a good baseline understanding of this stuff.
The complexity of modern vehicles comes down to software coupling between the systems, which (to my knowledge) started with automatic transmissions, and then spread to everything else. In very modern vehicles, even the sensors register with the ECU and communicate on encrypted channels.
The reason for these measures is ostensibly security and quality, but automakers don't seem to mind the fact that it also makes many repairs more difficult or impossible.