The profiler shows GDScript functions automatically because that's what the GDScript module does.
In C++ NativeScripts (assuming that's what you use), this kind of thing is not automatic, and I believe Godot doesn't do that automatically on registered functions either.
You can, however, use the GodotProfiling helper: https://github.com/GodotNativeTools/godot-cpp/blob/master/include/core/GodotProfiling.hpp
GODOT_PROFILING_FUNCTION at the beginning of your function.
(which can be improved https://github.com/GodotNativeTools/godot-cpp/issues/378 )