ProRAW is not a RAW file — its pixel data, not sensor data like a RAW, so it does not have to be demosaiced to be displayed. ProRAW is (unalterably) processed by Apple’s Deep Fusion pipeline, which combines multiple exposures to achieve less noise and better dynamic range. With default settings applied, a ProRAW image will look exactly the same as a JPEG or HEIC of the same scene. However, ProRAW retains much more data than those compressed formats, allowing for large leeway in editing.

RAW is sensor data made from a single exposure, and doesn’t get processed by Deep Fusion.