I can't exactly pinpoint when the issue began but it was around the time I did the Google messages RCS download. I've tried all the fixes you can think of, including the help of a Samsung care pro tech but to no avail. It's not a must have but just a nice funtion I enjoyed with my screen off and on vibrate mode when I couldn't get to my phone right away. I even used the edge lighting fix app and followed the instructions to have color specific notifications and that didn't work plus I wasn't to fond of sharing the permissions required with the third party developer. I'm giving up on a fix and just dealing with it for now. Hopefully soon there will be a permanent fix that doesn't require downloading an app.
Edge lighting fix by Zunderstruck is the only solution i know of. Edge lighting off screen is broken on galaxies because of overlay and notification prioritizing issues within the os code. Unless you really dont want to use the app, grant it permissions in the notifications section of the settings app, as well as in the Manage Notifcations within edge lighting. Also to make it work properly, in the By Text portion of the edge lighting Custom Color selection, write out the main title of the google rcs messages notifications and assign it a color. Thats how you make it work, not just by having it in the By App selector. Finally go into Apps>google message>notifcations and set all the notification style sub-categories you want to Sound And Pop-Up.
