2x and 8x image processing

I would like to know if anyone here has any information or has an understanding about how the camera on an iPhone 17 or 18 Pro handles non-optical lens photos during exposure. I am referring to 28mm, 35mm, 2x and 8x setting on the camera. Do these settings get special image processing or are they simply digital zooms. I get that Apple calls these Optical Quality zooms, but what does that mean? Are they handled differently than if I rotated the zoom wheel to say 42mm. A 24mm shot uses the Main lens and is 48MP. A 48mm shot uses the same lens, but it is only a 12MP photo. Because it only uses the center portion of the sensor. So if it is using the same 48MP sensor, does the camera do anything different than at 28mm, 35mm or 48mm? The same question holds for between 4x and 8x.

When I have done a test to answer this question, the ones not taken from 0.5x, 1x and 4x, the photos tend to be of a lesser quality. 28mm, 35mm, 2x and 8x, seem to do a pretty good job, but not like a true 48MP optical lens. All in-between digital zooms seem to suffer the most.

So, does anyone have any idea what is going on with any photo that is not taken with one of these three prime optical lenses or the 28mm, 35mm, 2x and 8x settings?

Thank you!

28mm, 35mm, 2x & 8x image processing/handling