Objective-C, the main difference to NeXTSTEP is that DriverKit changed from Objective-C into C++ with IO Kit, that uses Embedded C++ in a COM like approach.

In an homage to NeXTSTEP, the userspace version of IO Kit is named DriverKit.

There are some frameworks that might use C++ in their implementations, like Core Audio, however they are exposed to userspace as C APIs and Objective-C frameworks.

Hence why Apple nowadays mostly cares about LLVM, clang is good enough for their limited uses of C++.

https://developer.apple.com/xcode/cpp/

https://cppreference.com/w/cpp/compiler_support.html