Android P feature spotlights: System UI Tuner is nowhere to be seen
The System UI tuner has never really been a feature for the masses. It was a way of hiding experimental features from the majority of users — you had to long press the quick settings cog to activate it — while still letting the more inquisitive of us play around if we wished. In the early Oreo developer previews there were quite a few interesting things in there, but by DP3 it was reduced to just a couple of status bar and DND settings.
Android P feature spotlights: System UI Tuner is nowhere to be seen was written by the awesome team at Android Police.