Actually, the packaged SWI-cpp.h is the original interface by me. I’m a lousy C++ programmer though. Volker wrote something that is closer to how C++ programmers might want to see Prolog. I have little opinion on that 
But yes, the packaged one is maintained and since recently works cleanly using g++-11 on very high warning levels. It doesn’t do much more than a bit of basic type conversion and exception forwarding though. It also doesn’t cover the entire SWI-Prolog C API, but you can freely mix the two in you C++ code.