I use STM32F429-DISC1 which is pretty much the same as DISCO.
I cloned sample port but it was not compileable due to invalid target as per ac6 system workbench.
Following the text for setup works fine to build and run and importing files as per need from sample code results an OK project.
When I disable SDRAM build does not fit in RAM as your text suggests #define TFT_EXT_FB 0 /*Frame buffer is located into an external SDRAM*/
Would it be possible to split frame buffer and send in portions to ILI controller since it has its own GRAM anyway?
The Discovery board uses the MCU’s LTDC interface. So it is not connected via parallel port to the ILI controller but via RGB interface (HSYNC, VSYNC, colors). Therefore the MCU needs to contain the frame buffer.
On your custom board you can use parallel port to store the framebuffer in the ILI chip and allocate only a small buffer for LittlevGL.