you may use c++/latest, but it will only work for platforms where your compiler supports it.
Afaik by defaul c++11 is enabled, as it’s the greatest version that is supported by all possible target platforms.
If you don’t want any problems with compatibility (including some 3rd party plugins), then it’s reasonable to keep default version set. If you going for pc only\research purposes, then i think c++/latest is a possible choise.
This setting is a per-project and is set in YOURPROJECT.build.cs, like
CppStandard = CppStandardVersion.Cpp14; //another possible options are "Cpp17", "Latest", not sure about 20