Problems using TArray "Left of ... must be a Class/Struct/Union"

Hello there, I’m new to UE.

I’m having issues with TArray - the Compiler doesn’t seem to recognize any of the TArrays I’m trying to use in my cpp project,
giving me the C2227 Compiler Error mentioned in the title.

The IntelliSense does suggest all the appropriate functions, but whenever I try to call one on an instance of TArray, the compiler just doesn’t recognize the instance as a class at all.
Is this a common problem with UE (and what am I doing wrong most likely?) Does it make a difference, if the type of the array elements is UCLASS / USTRUCT or regular c++ classes?

Here’s what’s in my Project’s .cs-File:
PublicDependencyModuleNames.AddRange(new string] { “Core”, “CoreUObject”, “Engine”, “InputCore” });
PrivateDependencyModuleNames.AddRange(new string] { });

And the Project header only has
#include “Engine.h”