The Chinese tech giant Oppo has leaked a patent recently that describes that the company is gearing up to use a rear mounted secondary display. The Chinese National Intellectual Property (CNIPA) has published this report and the design patented in the publication shows that the phone will have a circular camera setup same like Huawei Mate 40 which has three sensor accompanied with LED flash as well. A tiny circle shown inside the donut design is actually a tiny secondary display.
The patent suggests that the secondary display will likely to show the date and time. The patent also reveals that there will be no selfie camera which suggests that the secondary display will double as a viewfinder while taking selfies. No more detail is described in the publication in this regard.