That’s a great idea! I remember on an Android phone - maybe Galaxy Nexus, or the original Pixel - you could blink an LED with different colors for different app notifications. I had blue, yellow, red, and green for various apps, and so without ever having the screen turn on or the device make sounds, I could tell if I should bother to check.
To me, not having any sensory disabilities, that’s a lower cognitive load than banners or other text/icon-based notifications.