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.
Depending on the RAW, a conversion to DNG may not be lossless.