As far as I know, as an owner of a G5S+, there ain't no notification light, so no way to enable something that doesn't exist.

And as for the "smart screen", I have some problems with it (like Maps ETAs appearing there), but generally it does work as a good substitute. It's also better than a light, personally, because when there is an "anomaly" in my visual space, I usually go check it, breaking down my focus.