OnePlus users have been asking for the always on display feature for quite some time now, and it looks like it could finally arrive with the OxygenOS 11 release later this year. An open beta test is scheduled for September. OnePlus recently teased the look of the interface, which includes a thin gradient line running down the center of the screen.
https://www.notebookcheck.net/OnePlus-to-finally-introduce-always-on-feature-for-its-phone-displays-with-the-OxygenOS-11-release-in-late-2020.484266.0.html