IOKit and all drivers, which are most of the iOS kernel by lines of code, are C++. The windowing system of iOS and modern macOS, Core Animation, is a hybrid of

IOKit and all drivers, which are most of the iOS kernel by lines of code, are C++. The windowing system of iOS and modern macOS, Core Animation, is a hybrid of Objective-C and C++. As pointed out by the sibling comment, core Android—everything Google wrote except kernel modules—is basically all C++. Vulkan is a C API (though might have a C++ implementation), but Metal is all Objective-C (with internals written in C++, I think?), and Direct3D is all COM-flavored C++.