Objects not found in OpenCV4 - c++

Question

This is my dir tree (root dir is untitled)
This is the content of CMakeLists.txt
cmake_minimum_required(VERSION 3.0.0)
project(untitled)
set(CMAKE_CXX_STANDARD 11)
find_package (OpenCV 4.5.2 REQUIRED)
include_directories ("/usr/local/include/opencv4/")
add_executable(untitled main.cpp)
This is my code in main.cpp:
#include <iostream>
#include <string>
#include <sstream>
#include <opencv4/opencv2/core.hpp>
#include <opencv4/opencv2/highgui.hpp>
using namespace cv;
using namespace std;
int main(int argc, const char** argv) {
Mat color = imread("./lenna.png");
Mat gray = imread("./lenna.png", 0);
imwrite("./lennaGray.png", gray);
int myRow = color.cols - 1;
int myCol = color.rows - 1;
Vec3b pixel = color.at<Vec3b>(myRow, myCol);
cout << "Pixel value (B, G, R): (" << (int)pixel[0] << ", " << (int)pixel[1] << ", " << (int)pixel[2] << ")" << endl;
imshow("Lenna BGR", color);
imshow("Lenna Gray", gray);
waitKey(0);
return 0;
}
This is the entire error when I ran make command:
But if I ran my code in terminal by this command:
g++ main.cpp -o main -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_imgcodecs -I/usr/local/include/opencv4 && ./main
then it worked.
I don't know what happened, I just learned OpenCV and I am using Ubuntu 20.04 and OpenCV-4.5.2.