Is there a way to mod this version? (greater diplomacy 4 doesn't load on y computer)
If you go to the google docs that stores the Greater Diplomacy SB3 data, you can just scroll down until you get to the Legacy Versions, and download the SB3 data for Greater Diplomacy 3 there.
If you don't feel like doing all that, you can also just get the SB3 file here: https://drive.google.com/file/d/1RIhyo-Ply3b1aCSCuATQJxrjmKcWLoMZ/view?usp=drive_link