Hi aetuo,
Good point, the bcm2835 library isn’t needed if the driver is compiled in I2C mode (I played with both the modes at the beginning and copied both the commands). I’ve just removed that step.
Which error do you get when you try to install OpenCV on Raspberry? I also use a RaspberryPi 4, the installation method through pip should be much more straightforward than on previous models: https://www.pyimagesearch.com/2019/09/16/install-opencv-4-on-raspberry-pi-4-and-raspbian-buster/.