Bom dia, segue meu código abaixo:

main.js

const { app, BrowserWindow, ipcMain } = require('electron');

app.on('ready', () => {
  console.log('Papa Recall');
  let mainWindow = new BrowserWindow({
    width: 1280,
    height: 800
  });

  console.log(__dirname);
  mainWindow.loadURL(`file://${__dirname}/app/index.html`);

});

app.on('window-all-aclosed', () => {
  app.quit();
});

let sobreWindow = null;

ipcMain.on('abrir-janela-sobre', () => {
  if(sobreWindow == null){
      sobreWindow = new BrowserWindow({
        width: 300,
        height: 220
    });

    sobreWindow.on('closed', () => {
      sobreWindow = null;
    });
  }
    sobreWindow.loadURL(`file://${__dirname}/app/sobre.html`);
});

package.json

{
  "name": "paparecall-app-desktop",
  "version": "1.0.0",
  "description": "",
  "main": "main.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "electron . /main"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "electron": "^6.0.8",
    "electron-packager": "^14.0.6"
  }
}

renderer.js

const { ipcRenderer } = require('electron');

let linkSobre = document.querySelector('#link-sobre');

linkSobre.addEventListener('click', function() {
  ipcRenderer.send('abrir-janela-sobre');
});

porém a janela "sobre" não está abrindo.