ProRAW is Apple's version of the RAW image format, but it's not a true Bayer RAW image. Traditional RAW images are not intended to be viewed immediately since they're just the actual data that is captured by the camera's sensor — they need to be processed and edited to your liking. Think of it as "cooking" up a photo before it's ready to be consumed. When you shoot in HEIC or JPEG with your iPhone, you're basically allowing Apple's computational photography algorithm to "process" the image first so that it looks good enough without any further editing, though that's always a possibility.
With ProRAW, it's like a hybrid of Bayer RAW and JPEG/HEIC. When you shoot with ProRAW, you're getting a 12-bit RAW DNG file with 14 stops of dynamic range. ProRAW format allows Apple to use its signature computational photography features while still giving us as much of the pure data as possible to use in editing. Of course, with all of this data in the image, ProRAW files will be fairly large — an average of 25 MB each — whereas the usual JPEG could be around 3-5 MB, a HEIC could roughly be 1-3 MB on average, and a Bayer RAW about 10-15 MB.
So while ProRAW is a great new feature that gives you even more control when it comes to editing your photos, keep in mind that they are much larger in size.
It's important to note that the only devices that are capable of using Apple's ProRAW format right now are all the iPhone Pro series - starting from the iPhone 12 Pro/Pro Max and latest devices. If you have the regular iPhone 12 or iPhone 13, iPhone 12 mini or iPhone 13 mini, or an older iPhone, then, unfortunately, you can't shoot in ProRAW.
However, both our Reeflex Pro Camera and ReeXpose apps allow you to shoot in the traditional Bayer RAW format on any iPhone running on the latest iOS system. Keep in mind that the regular RAW format will lack the same computational photography that Apple uses for its ProRAW format so the photos will show as a real "raw" image, not elaborated and therefore needing to get processed in post-production (on Lightroom, Darkroom or other editing software).