This problem is due to wrong link between build folder & entry point of your app
DON’T USE in this way
mainWindow.loadURL(isDev ? ‘http://localhost:3000' : `file://${path.join(__dirname, ‘../build/index.html’)}`);
USE IN THIS WAY
mainWindow.loadURL(isDev ? ‘http://localhost:3000' : `file://${__dirname}/../build/index.html`);