Missing files after following the official installation instructions

C++
17

This is my CMake file:

cmake_minimum_required(VERSION 3.22)
project(mediafile_device_crossverification)

set(CMAKE_CXX_STANDARD 11)

set(OpenCV FOUND 1)
find_package(OpenCV REQUIRED)

add_executable(mediafile_device_crossverification main.cpp src/VideoProcessing.cpp src/VideoProcessing.h)

I’ve added

set(OpenCV FOUND 1)
find_package(OpenCV REQUIRED)

later on but it didn’t work.