Windows uses a special resource section in the exe to define an icon file. You can probably make nim add it like: [https://forum.nim-lang.org/t/4353](https://forum.nim-lang.org/t/4353) \- I have never done this though...
In the past I used rcedit.exe [https://github.com/electron/rcedit](https://github.com/electron/rcedit) to add the icon to the exe file after it is already built. rcedit "path-to-exe-or-dll" --set-icon "path-to-ico" Run Note you need a special .ico file, that can be created using an ico editor. There is an online ico editor you can use: [http://www.xiconeditor.com](http://www.xiconeditor.com)/ Just upload your probably-PNG icon to that. Make sure you have all of the versions from 16x16 to higher ups.
