With the iPhone 12 Pro, if I enable DNG & shoot in Pro mode the image in live view looks normal. Once the photo is taken it still looks normal (thumbnail in the bottom lefthand corner). It looks normal after tapping on the thumbnail & viewing it larger. However, once you go to Edit mode the same image is overexposed by a stop or more. It happens every time. (Yes, I know how to use the highlight clipping zebra stripes to see if the highlights are overexposed in the live view so no, I'm not overexposing). I'm using iOS 14.4 on an iPhone 12 Pro. I believe many people have this same issue on their devices. Is there a fix coming soon?
We cannot change how the sensor in each iOS camera provides raw image data. As the sensors have become larger over the last few years, the apparent overexposure you're talking about has become more pronounced. In the current LR 6.1 app for iOS, our developers made a change to the LR Capture viewfinder to create a more realistic impression of what final DNG raw captures will look like. This was done by disabling HDR in the capture viewfinder video feed to minimize exposure and dynamic range deltas. (The HDR viewfinder remains enabled for HDR capture.) Unfortunately, iOS platform APIs don't allow us such control of the viewfinder for older devices. Only devices with A12 or newer processors can see the viewfinder improvement (eg., iPhone XR or newer).
With the viewfinder improvement, on can then use exposure compensation (drag finger left <> right across the camera screen for -3.0 -- 0 -- +3.0 exposure compensation control). And then after capture apply Auto or other custom settings in Edit mode to get the DNG looking how you'd expect. I find myself shooting in HDR mode often, as the final results get automatic processing the basic DNGs do not. I rely on DNG at times, eg., when I need contrast. I might shoot several shots with different exposure compensation settings, and then find the best result later.
BTW, the capture review image you mentioned is actually a processed JPG thumb that is not the actual DNG raw image, which is why DNGs look different when browsing and editing them later.