OnePlus maintains a somewhat common codebase for its Android-based OxygenOS software across all its devices for the sake of easy maintenance and interoperability. Take the example of the highly anticipated Always on Display mode: It has finally appeared in the latest OxygenOS 11 developer preview builds for the OnePlus 8 series, and the OEM has promised to bring this feature to other OnePlus smartphones in the coming update. However, the company did skip backporting the "Horizon Light" notification feature to the OnePlus 6T.

OnePlus 6T XDA Forums

For those not familiar with Horizon Light, OnePlus designed this feature to show a pulse on both sides of the display when a notification arrives. This edge lighting functionality is available on all OnePlus phones with curved screens starting with the OnePlus 7 Pro, which means it is accessible on both the OnePlus 7T Pro and the OnePlus 8 Pro but not on the OnePlus Nord.

XDA Senior Member mcdachpappe has now come up with a Magisk Module that can enable Horizon Light on the OnePlus 6T. The working principle of the module is quite simple: It replaces the stock System UI APK of OxygenOS with a modified one. After flashing the module via Magisk Manager, the edges of your OnePlus 6T should light up five times per notification. The color of the pulse corresponds to the color of the app-icon which generates the notification, e.g. green for WhatsApp. There is no user interface for this mod, though, so you can't modify the hardcoded parameters (lighting frequency, color, etc.).

Magisk Module to enable Horizon Light on OnePlus 6T - XDA Thread

The initial version of the module is tested against OxygenOS 10.3.5. The mod has yet to support dynamic resource patching, which is why you may need a new build when OnePlus pushes the next OxygenOS update for the OnePlus 6T.