Pixel phones and I believe Samsung phones just light up the OLED display to let you know that there is notification. An independent LED was only necessary because screens would have to light up the whole display to indicate notification,but now we have better screens so that isn't necessary.
I have a Samsung and have it set to light up the screen but it's not the same as that LED. I used to be able to set the LED color for messages from certain people. Ex: Blue was a friend, Red was mom. The LED would also stay that color until I read the message where as the current screen color only lights up for a few seconds (unless there is a setting I'm missing).