Oppo recently obtained a patent from WIPO (World Intellectual Property Organization) for a device with a UD camera and a small screen on the back, in addition to the main camera setup.
The patent has been filed with and with CNIPA (Chinese National Intellectual Property Association), but has only recently been approved for global use.
LetsGoDigital in its report reveals a curved screen from all four sides, and a square rear camera with four cameras inside. The thing to note is that the number of cameras in the filing is not part of the patent because it is only an illustration.
The second display is here to help selfies and display notifications. Having a screen next to the camera goes back to the Meizu 7 Pro series and was recently adopted by the Mi 11 Ultra, allowing them to take selfies with the main camera.