Example interface in Unreal Engine 5.

Example Usage.cpp

AActor* ActorToUse = /* Get the actor that implements the ItemInterface */;

if (ActorToUse && ActorToUse->GetClass()->ImplementsInterface(UItemInterface::StaticClass()))
{
    IItemInterface::Execute_Use(ActorToUse);
}

ExampleCppImpl.cpp

#include "ItemActor.h"

AItemActor::AItemActor()
{
    PrimaryActorTick.bCanEverTick = true;
}

void AItemActor::Use_Implementation()
{
    // Default C++ implementation, can be empty if you want to force Blueprint implementation only
}

ExampleCppImpl.h

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "ItemInterface.h"
#include "ItemActor.generated.h"

UCLASS()
class AItemActor : public AActor, public IItemInterface
{
    GENERATED_BODY()

public:
    AItemActor();

    UFUNCTION(BlueprintNativeEvent, Category = "Item")
    void Use();
    virtual void Use_Implementation() override;
};

ItemInterface.h

#include "CoreMinimal.h"
#include "ItemInterface.generated.h"

class IItemInterface
{
    GENERATED_BODY()

public:

    UFUNCTION(BlueprintNativeEvent, Category = "Item")
    void Use();
};