The conclusion is rather dismal. The area in the screen under which the selfie camera resides is noticable - in fact the reviewer say that the "under-display integration is extremely noticeable on light backgrounds". You can see a square patch of the screen that exhibits a clear dithering effect. In fact the reviewer says that he'd prefer a notch-type display over what he gets in the Axon 20 5G.
Another problem is that the quality of the selfie camera is quite low. According to the review it is clear that while an under-the-display camera is a nice gimmick - it doesn't really make sense in any way - at least until the technology is improved considerable.
In July Chinese OLED producer Visionox launched its under-the-OLED camera technology, branded as InV See. According to reports from China, Visionox is supplying its InV See displays to Xiaomi and also to Huawei. It is likely that ZTE is also using a Visionox OLED in the Axon 20 5G.