Android P prevents Substratum themes from being used
Substratum is a rootless way to install custom themes on Android Oreo. When it burst onto the scene around September of last year, it instantly became a crowd favorite; people loved the ability to reduce the increasing amount of whiteness Google was shoving into Android. However, it seems like Google wasn’t happy with this, as Substratum and custom overlays in general are no longer functional on Android P.
The lead Substratum developers have confirmed that many are seeing this issue.
Android P prevents Substratum themes from being used was written by the awesome team at Android Police.