Actually, like everything in computing, it depends.
Reference counting is a form of garbage collection, as per most highly referenced CS books on the subject, like The Garbage Collection Handbook, chapter 5.
https://gchandbook.org/
But lets put that aside, considering that std::..._ptr<>() or any other variant thereof are plain optional library types.
That still leaves Unreal C++, C++/CLI, C++/CX as garbage collection extensions to C++, just like GCC C++ or clang C++ provide their own language extensions.
https://docs.unrealengine.com/4.26/en-US/ProgrammingAndScrip...
https://docs.microsoft.com/en-us/cpp/dotnet/dotnet-programmi...
https://docs.microsoft.com/en-us/cpp/cppcx/visual-c-language...