High shutter speed with low frame rate and auto exposure

Hi there,

I want to set the iphone camera to "S mode, or Shutter Priority" in camera terminology. Which is a semi-auto exposure model with shutter speed fixed, or set manually.

However, when setting the shutter speed manually, it disables the auto exposure.

So is there a way to keep the auto exposure on while restrict the shutter speed?

Also, I would like to keep a low frame rate, e.g. 30 fps. Would I be able to set shutter speed independent of frame rate?

Here's the code for setting up the camera

Best,