Prior to the Android 11 Update I was using an App called Lightflow. You can customize the blink rate and color of the LED for the notification of all installed apps individually.
HOWEVER: After the Android 11 update the app still works, but now it is vibrating one time when switching the screen off and every time you receive a notification. Haven't found a way to turn that off. Came after the Android 11 upgrade and seems to have something to do with the how notifications are done.
Gave up on it, another thing an update broke on a perfect running phone before the update.