I say you actually need to make step backs, as with UE4 you don’t use standard library and STL, UE4 has it own standard library, primerly for multi platform support (it makes sure that UE4 game code will build on any platform with any compiler that UE4 supports) and possibility to monitor code activity and easy adaption to optimization as everything (but only conventionally) is forced to go thru UE4 code and by that UE4 knows what you code is doing.
So i would say you more then ready, you only need to know about syntax and primitive features, you will need forgot about standard library and relearn APIs anyway.
That said you could use C++ standard library, don’t think it some special “UE4 C++” because it isn’t, it is normal C++ just different core libraries and some extra automated code generation tool assistance (UnrealHeaderTool) and use of standard C++ library is not recomanded, UE4 is not even compatible with it anyway but you may end up need to use it when you try to use 3rd party libraries. But oyu would need to wrap it to UE4 APIs.