electron: Failed to load URL: http://localhost:3000/main_window with error: ERR_CONNECTION_REFUSED in production mode – Ubuntu

With the executable (yarn make) I get this error :

electron: Failed to load URL: http://localhost:3000/main_window with error: 
ERR_CONNECTION_REFUSED

This error does not show up in the development mode

I tried to differentiate between dev and prod modes in main :

 import isDev from 'electron-is-dev' 
 const createWindow = (): void => {
  // Create the browser window.
  const mainWindow = new BrowserWindow({
    height: 600,
    width: 800,
    webPreferences: {
      preload: MAIN_WINDOW_PRELOAD_WEBPACK_ENTRY
    }
  });

  // and load the index.html of the app.
  isDev ? mainWindow.loadURL(MAIN_WINDOW_WEBPACK_ENTRY) : `file://${path.join(__dirname, '../build/index.html')}`

  // Open the DevTools.
  if (isDev ) {
    mainWindow.webContents.openDevTools();
  }
};

but in this way the error message doesn’t show up, but also the correct window’s page Electron App doesn’t show up :

In Development Mode : "Got Finally!!" message in the window’s page is present,

but not in Production Mode

meaning that the page is not correctly loaded

Other Info:

Electron: 19
O.S. : Ubuntu 22.04

How to make it work?

Update 1)

Thanks to @Bets comment I realized I made two mistakes (the folder and the ternary operator) and I updated the line of code accordingly:

mainWindow.loadURL(isDev ? MAIN_WINDOW_WEBPACK_ENTRY : `file://${path.join(__dirname, '../renderer/main_window/index.html')}`)

The folder this time is correct:

console.log(path.join(__dirname,'../renderer/main_window/index.html')) =>
/home/raphy/ForgeTypescriptReactWebpack
/out/forgetypescriptreactwebpack-linux-x64/resources/app/.webpack
/renderer/main_window/index.html

raphy@raohy:~/ForgeTypescriptReactWebpack/out/forgetypescriptreactwebpack-linux-x64/resources/app/.webpack/renderer/main_window$ ls -lah
total 3,5M
drwxrwxr-x 2 raphy raphy 4,0K gen  4 12:17 .
drwxrwxr-x 3 raphy raphy 4,0K gen  4 12:17 ..
-rw-rw-r-- 1 raphy raphy  386 gen  4 12:17 index.html
-rw-rw-r-- 1 raphy raphy 3,4M gen  4 12:17 index.js
-rw-rw-r-- 1 raphy raphy 1,8K gen  4 12:17 preload.js

but, still, the page is not correctly loaded and not getting the right output