How "unfiltered" raw-ish data can you get on the iPhone in an app?

It's Bayer RAW: not yet demosaicked sensor information from a single exposure, without any of the extra steps you get shooting a format like HEIC/JPEG (or even ProRAW [0]), where lots of additional processing is done, including combining multiple frames to get extra dynamic range, detail, reduced noise, etc.

There's still some amount of denoising/sharpening/etc happening in the ISP, but essentially shooting Bayer RAW gets you the output of just the small first part of the pipeline, rather than the whole pipeline.

[0] Despite the confusingly similar names, Bayer RAW and Apple ProRAW are quite different - I wrote about it on this page because I frequently get emails from confused customers.

https://bayercam.com/understanding-bayer-raw