Testing on a desktop machine with many cores is not a good simulation of that environment. You run your tests on your local machine as much as possible. Then you run on the real production hardware enough tests to be confident.

I don't work automotive, but my application is very similar - an embedded display running ARM CPUs. I do a lot of testing on x86-64 and only rarely encounter portability issues. When I do discover such things they have always been things that I need real hardware to debug on not something an ARM desktop would help with.