I would recommend you to use a newer C++ standard in ROOT, because there I know better what is going on.
You can re-build also the current ROOT version that you are using with CMAKE_CXX_STANDARD 17. The C++ standards listed in the page you linked are only the minimum supported C++ standards by the different ROOT versions. For example, ROOT 6.30 can’t be built with any standard older than C++17 anymore.