JAVASCRIPT

default Electron icon is used reason=application icon is not set

//Create a folder named build in the same directory of package.json
//place your icon inside (it has to be named icon)

//in the package.json (variuos options are examples, not mandatory):
"build": {
    "appId": "com.SUPPLIER.APP_NAME",
    "mac": {
      "category": "public.app-category.utilities",
      "target": "dmg"
    },
    "extraResources": [
      "res",
      "favicon.png"
    ],
    "directories": {
      "buildResources": "build", //<-- this is important
      "output": "output"
    }
  },