Larian Studios Forums Divinity: Original Sin 2 - The Modding Dungeon Divinity - Original Sin 2 - Modding Troubleshooting Cannot Rename Project

This seems bugged for me too. A workaround is to create a new level with your desired name and then delete the contents of the new level folder in (the Game folder) Mods/ProjectName/Levels/LevelName and Editor/Mods/ProjectName/Levels/LevelName and copy the contents of the old ones into the new ones.