The installer itself doesn’t provide any method to extract files or the script without installation. It is the developer’s choice whether the source code and/or the files for the installer are available to the public or not. External tools that allow this include 7-zip, InstExpl and Universal Extractor. The decompression plug-in InstExplorer InstExpl.wcx is also available for TotalCommander. Beside the files it’ll create the file’script.bin’ compiled scriptcode.”]
Source: https://nsis.sourceforge.io/Can_I_decompile_an_existing_installer