Why does iPad Pro Gen4 does not allow portrait mode on the back camera?

“Portrait Mode” is principally an iPhone feature that uses a combination of camera lenses - and software processing - to combine images to produce a bokeh effect.

This feature requires specific lens and CPU hardware for processing the image data - which is not available on earlier versions of iPhone and iPad.

We are all users on this forum. No iPad supports portrait mode. iPad is not exactly a good form factor as a camera. But why Apple doesn't include portrait mode however, is only known by Apple and since no one here works for Apple we can only guess.