Notably, you have to go back to 70’ish era to get that kind of equipment. Almost everything else has some kind of ECU.
Cellular connections didn’t start becoming somewhat common until the late 90’s-early 2000’s though.
E.g. 5th gen Toyota 4Runners: https://www.4runners.com/threads/how-to-disconnect-the-track...
If one wants to buy a modern car, and one cares about preserving disconnected functionality, one just needs to research if there's a workable fallback mechanism.
Or, you know, deal with the 20mpg but a vehicle that will last until the heat death of the universe #2uzfeClub
FWIW while cars are essentially backdoored nowadays with all the cellular/OTA updates BS you can still disable it. I suspect this won't be an option in the near future, the way things are going.
I can't wait to see Hacker News comments in 2035 lamenting how they used to be able to "just use a bypass cable" to make their cars not phone home, by the time EVs and even general ICE vehicles have telemetry so deeply integrated with the vehicle it's impossible/illegal to be disabled.
I also have 2008 mazda3. Great reliable car. Also no connectivity whatsoever.