: You cannot open "part18" on its own. You need every single part (part1, part2, etc.) in the same folder to extract the game.
The naming convention tells a very specific story about what this file is and where it came from: Baldurs.Gate.III.v4.1.1.1695932.GOG.part18.rar
📍 : This file is just one piece of a giant puzzle; without the other parts, it is functionally useless data. : You cannot open "part18" on its own