Yes, this can be a bit confusing. RAW Processing is always “on,” using the default values.
The default values are not the same for every image. They come from Apple’s analysis of the camera and the image. Apple will adjust the black point, noise, and other settings as part of their attempt to make the image look good. If you want to change what they have done, you would move the sliders in RAW Processing. If you want to see the default decode, then you can uncheck the box.