GENERATED_BODY() sets all members private, but UPROPERTY with BlueprintReadWrite or BluePrintReadOnly need to be public.
Try to change it like this:
GENERATED_BODY()
public:
UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "Hero")
float Health = 100;
UPROPERTY(BlueprintReadOnly, VisibleAnywhere, Category = "Hero")
bool isDead = false;
private:
...