How does the Pico Omnibus work?

I purchased a pico omnibus after realizing my display pack didn’t leave any pins for GPIO, but I haven’t been able to find any documentation online regarding how it is intended to be used. I want to have some jumper cables interfacing with an external ADC on one of the decks, with the display on the other but both decks seem to output the same values constantly. Is there a way to select one deck or are they always tied together?

It is wired pin for pin.
It’s the equivalent of stacking one deck on top of the other.
Any signals to or from the Pico will appear on both sides.
The pins are labeled as to what they are.