I used to fly on planes that had “fancy” controllers - they had lots of buttons (full QWERTY keyboard, ABXY and d-pad, special buttons for controlling the lights and calling the attendants, etc.) and slotted into a latched recess right below the IFE. Something like this: https://www.vecteezy.com/photo/11024929

There’s no analog stick and the ergonomics aren’t that great, but it’s definitely usable as a controller.