Though this is tested on Oneplus 6T, it should be working for most Android Oreo and later phones.
So I was annoyed not having an LED notification light on OnePlus 6T and I tried to make one of my own.
With phones having AMOLED display whenever a desired notification comes the app brings in a black screen with notification LED looking animation.
To use it:
1. Disable Ambient Display and any battery optimisation for the app.
2. Give notification access permission.
3 Select apps you want notifications for, by choosing a color
Note: On successfully selecting a color for an app the text in which the App name is written should change to that color
Thats it