I don't get this in particular. All of these devices have C, which seems like a better fit for the problems you'd likely have on a platform that's small or obscure enough that it hasn't got something nicer than C++

For anything weirder than that (PIC?) where Rust is no option, it's not like you have no choice either: You can just pick C.

But isn't using Qt like learning a whole new layer of language on top of C++, the meta compiler, signal/slot system etc and then Qt have its own set of standard classes like QString (instead of using std::string)