mbed is a toy, at the same professional level as Arduino, although ARM does a better job of marketing as something much more serious.
However, AutoSAR is a fair point. There are a lot of hands in the pot on that and them coming to an agreement to use C++ is rather surprising - counterpoint that Automotive ECU code is absolutely HORRIBLE right now and no one seems to know it. I work in Auto and all the mfgs have moved to a fix in the field model. It’s really bad, and I wouldn’t touch a first year new model for any reason.
So while AutoSAR C++ is interesting, this isn’t exactly the group that I want to model myself on.
AUTOSAR moved from C to C++14 as the certified language.
mbed is written in C++.