Problem

I'm working on a Marlin-based Arduino firmware that compiles and runs perfectly with the RepRapDiscount Smart Controller (standard 20x4 text display), but I want to switch to a RepRapDiscount Full Graphic Smart Controller (128x64 ST7920).

As soon as I change the display type in Configuration.h, the code fails to compile.

My goal

I want the exact same functionality and menu layout as with the normal LCD, but on the Full Graphic Display.

Important note

⚠️ I'm not experienced in programming.
I'm using this project for school, and I'm trying to get it working with a graphical display. I don't understand all parts of the firmware, especially the custom menu rendering.

Any help or suggestions would be very much appreciated! 🙏
Thank you!