BBC writes about cars and viruses. The title is " Cars safe from computer viruses" and it tells a story of a test of one(!) car model with one(!) virus. An attempt to infect a car with a virus written for a phone (using a different operating system) failed, so the conclusion is that cars are safe...
I will add that infecting one OS with a virus written for another is possible only in very special cases.
The test shows only that that car model is not infected by that one virus. Nothing more.