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
For MIUI 11 devices make sure that AutoStart is enabled in App Info. Also check “Show on lock screen” permission in other settings.
Settings image: https://drive.google.com/folderview?id=1yxrLd5u7kLSGBwviKhXYqM21YLC8Dhiv