The ST is more likely a boost converter, look at the inductors around it.
Too few pins to be a oled display-driver
look again, there are no traces routed from those, so I don’t think any data is travelling through those. It’s just ground.
any relevant high-speed bus wouldn’t work well routed in that manner.
main board is the “computer“ where all the flexes come in to connect to screen & peripherals.
the rf-board is purely networking so very few wires has to connect between the main ARM and that board.
You are all wrong :-) look at the RF board, there isn’t a signle trace routed from the armada of solder-pads, so I’d say they’re purely mechanical & GND /tekhead