Objective-C only became relavant because of Apple, and even so, macOS has more lines of C++ code than BeOS.

Objective-C driver subsystem from NeXTSTEP was replaced by C++, and plenty of subsystems are written in Objective-C++.

Metal uses C++ as shading language.

As ex-Nokian, Symbian failed not because of Symbian C++, but because of management and internal politics.