The iOS camera format control is one of the most confusing UIs in iOS. It first asks you to select between high efficiency and most compatible (HEIF vs JPEG). Then it asks you whether you want ProRAW. Then under ProRAW it asks whether you want JPEG lossless, JPEG XL lossless or lossy. That doesn’t even include the in-app control of JPEG Max (which AFAIK is just 48 MP JPEG).
Raw photos probably are shot in DNG. DNG "images" are popular for raw images because theyb can be losslessly converted from to the camera raw formats like the Nikon's, and DNG is open source and royalty free.
Natively it’s coming off the sensor like everything else, raw 8-16bit values. The OS then takes that stream and packages it into whatever, which on iOS can be a DNG, optionally pre-debayered with ai stuff in it (proraw), or just a standard, bayer mosaiced DNG, or JPEG, or HEIF, or JPEG XL.
Depending on the RAW, a conversion to DNG may not be lossless.
And unless I missed something, the default Camera app doesn't support "unprocessed DNG" - you need an app like Halide. Camera app only does JPG/HEIC or ProRAW. And as the sibling comment says, it's a confusing UX, split between the Settings app and the Camera app. Not that it matters to most users, who only need/want the default HEIC.
