LCD Contrast Adjustment:
Once you have connected the LCD to an Arduino and uploaded the code, you might observe that the display appears all black or nothing is visible on the screen. There's no need to worry, as this behavior is normal. The contrast of the LCD needs to be adjusted. After wiring the LCD, you will need to adjust the contrast by using the potentiometer located on the I2C module. This potentiometer can be rotated using a small screwdriver.
Now, power on the Arduino. You will notice that the backlight illuminates. As you turn the knob of the potentiometer, the first row of rectangles will start to appear. If you have successfully reached this point, congratulations! Your LCD is now functioning properly.