Though this is tested on OP6T, it could be working for most Android Oreo and later phones.

As a lot of phones have AMOLED display whenever a desired notification comes the app brings in a black screen with edge lighting.

To use it:
1. Disable any battery optimisation for the app.
2. Give notification access permission.
3 Select apps you want notifications for, by choosing a color
Thats it.

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

Additional Features:
1. Change blink animation time.
2. Change edge colours.
3. Notify for missed calls.
4. Change edge radius to fit various screens
5. Add Downtime

// Option A //

To download NotifyEdge - Edge Lighting mod from HappyMod.com.
You need enable the option "Unknown Sources".
1. Click on the above link to download NotifyEdge - Edge Lighting mod APK.
2. Save the file in your device Downloads folder.
3. Now tap on Install and wait for the installation to finish.
4. Once it is done, open the game and start playing it right away.

// Option B //

To download NotifyEdge - Edge Lighting from HappyMod APP, you can follow this:
1. Open your browser and download the HappyMod APK file from HappyMod.com - the only official website of HappyMod.
2. Open Android Settings and go into Privacy or Security.
3. Tap the option to Allow Unknown Sources and enable it.
4. Go to your Android downloads and tap the APK file.
5. Follow the directions on the screen to install it.
6. Search NotifyEdge - Edge Lighting in HappyMod App.