We need a picture of the entire pcb. The ribbon cable (technically a flex pcb, not a ribbon cable) is totally custom and not something you can put a signal on. The little green pcb looks like the driver, so we would need pics of that and maybe figure out where you can input some kind of signal.
These kinds of displays can be really hard te re-use. Often their driver is just a simple blob (chip on board) which would be completely custom. This can be made cheaply to order with as few as 500 units. So mass produced readers often use completely custom stuff to get down to a really low price. Unfortunately this means it’s not possible te repurpose the screens later.
Spi is the norm for hobby displays because they are made to be driven easily. There is a driver chip that receives the spi signal and drives the display. With an actual product this often isn’t the case and the screen gets driven directly.