The instructions and code that you link to are for Sangaboard v0.3, or a system based on an Arduino Nano (ATmega328p).
Sangaboard v0.5 uses a different internal microcontroller to deliver the Sangaboard functions that are presented externally. This is an RP2040, as on the Raspberry Pi Pico microcontroller board. The firmware for that is different to account for the different architecture and is in a different repository. If you have purchased the board it is likely to already have the firmware installed. If you had the board made yourself then the loader linked in Sangaboard v0.5 now available - #2 by filip.ayazi might be appropriate, or other posts about the firmware in that thread might help. It is not something that I am totally familiar with.