: You cannot open "part18" on its own. You need every single part (part1, part2, etc.) in the same folder to extract the game.
: This refers to a specific version of the game, likely released around late 2023. Baldurs.Gate.III.v4.1.1.1695932.GOG.part18.rar
The naming convention tells a very specific story about what this file is and where it came from: : You cannot open "part18" on its own
: If you want the most stable, auto-updating experience, the official version is available on the GOG Store . Baldurs.Gate.III.v4.1.1.1695932.GOG.part18.rar