Ambient display is one of the best features found on Android devices, but unfortunately not every device has this feature available for it. Typically, the feature is available only for those devices with OLED displays (due to battery drain concerns) as the feature lights up a part of the screen to show incoming notifications. Some OLED devices even support an always-on mode, though this is rarer. But since the feature is available in Android's source code (AOSP), developers can include the feature on any Android device they choose.
To that end, XDA Recognized Developer Rizal Lovins created an overlay that can be installed on rooted Sony Xperia Z5 and Sony Xperia XZ devices that are running stock-based Android 7.1.1 Nougat ROMs. The overlay enables ambient display mode when a notification is received. Be warned that enabling this feature on an unsupported device with an LCD display may cause more battery drain than you might think.