This project is an arduino library for my M128/64 STK board. It is a developer board with a ATMega128a micocontroller on it.
Use the board manager with the custom board manager URL https://raw.githubusercontent.com/csutorasa/M12864STK/master/package_m12864stk_index.json.
You need to explore the latest release. Find the library you need and download the zip archive. Use the official guide to add this zip to the libraries in Arduino IDE.
The device can be flashed via ISP. A simple way is to flash the software with USBASP. You will need drivers for using it.