Yes, in my experience the most common usages are to pair an Objective-C Cocoa UI to cross platform C++ internals, to use C++ for more performance critical parts

Yes, in my experience the most common usages are to pair an Objective-C Cocoa UI to cross platform C++ internals, to use C++ for more performance critical parts of an app, or even to just be able to take advantage of the plethora of C++ libraries without going all-in on C++. Things might’ve changed with Swift being around now, but as I understand one place where the Obj-C UI + C++ internals setup used to be common was Audio Unit extensions due to the high latency sensitivity of anything working with audio.