From a tutorial using electron v9 though trying to get it to work with v12.2.3

AppTray.js

const { app, Menu, Tray } = require('electron');
// eslint-disable-next-line no-unused-vars
const MainWindow = require('./MainWindow');

class AppTray extends Tray {
    /**
    * Creates an instance of AppTray.
    * @param {string} icon
    * @param {MainWindow} mainWindow
    * @memberof AppTray
    */
    constructor(icon, mainWindow) {
        super(icon);

        this.setToolTip('SysTop');

        this.mainWindow = mainWindow;

        this.on('click', () => {
            if (this.mainWindow.isVisible() === true) {
                this.mainWindow.hide();
            } else {
                this.mainWindow.show();
            }
        });

        this.on('right-click', () => {
            const contextMenu = Menu.buildFromTemplate([
                {
                    label: 'Quit',
                    click: () => {
                        app.isQuitting = true;
                        app.quit();
                    },
                },
            ]);

            this.popUpContextMenu(contextMenu);
        });
    }
}

module.exports = AppTray;

main.js

const path = require('path');
const { app, Menu, ipcMain, BrowserWindow } = require('electron');
const Store = require('./Store');
const MainWindow = require('./MainWindow');
const AppTray = require('./AppTray');

// Set env
process.env.NODE_ENV = 'development';

const isDev = process.env.NODE_ENV !== 'production' ? true : false;
const isMac = process.platform === 'darwin' ? true : false;

/** @type {MainWindow} */
let mainWindow;
/** @type {AppTray} */
let tray;

// Init store & defaults
const store = new Store({
  configName: 'user-settings',
  defaults: {
    settings: {
      cpuOverload: 80,
      alertFrequency: 5,
    },
  },
});

function createMainWindow() {
  mainWindow = new MainWindow('./app/index.html', isDev);
}

app.on('ready', () => {
  createMainWindow();

  mainWindow.webContents.on('dom-ready', () => {
    mainWindow.webContents.send('settings:get', store.get('settings'));
  });

  const mainMenu = Menu.buildFromTemplate(menu);
  Menu.setApplicationMenu(mainMenu);

  mainWindow.on('close', (e) => {
    if (!app.isQuitting) {
      e.preventDefault();
      mainWindow.hide();
    }

    return true;
  });

  const icon = path.join(__dirname, 'assets', 'icons', 'tray_icon.png');

  // Create tray
  tray = new AppTray(icon, mainWindow);
});

const menu = [
  ...(isMac ? [{ role: 'appMenu' }] : []),
  {
    role: 'fileMenu',
  },
  {
    label: 'View',
    submenu: [
      {
        label: 'Toggle Navigation',
        click: () => mainWindow.webContents.send('nav:toggle'),
      },
    ],
  },
  ...(isDev
    ? [
        {
          label: 'Developer',
          submenu: [
            { role: 'reload' },
            { role: 'forcereload' },
            { type: 'separator' },
            { role: 'toggledevtools' },
          ],
        },
      ]
    : []),
];

// Set settings
ipcMain.on('settings:set', (e, value) => {
  store.set('settings', value);
  mainWindow.webContents.send('settings:get', store.get('settings'));
});

app.on('window-all-closed', () => {
  if (!isMac) {
    app.quit();
  }
});

app.on('activate', () => {
  if (BrowserWindow.getAllWindows().length === 0) {
    createMainWindow();
  }
});

app.allowRendererProcessReuse = true;

MainWindow.js

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

class MainWindow extends BrowserWindow {
  constructor(file, isDev) {
    super({
      title: 'SysTop',
      width: isDev ? 800 : 355,
      height: 500,
      icon: `${__dirname}/assets/icons/icon.png`,
      resizable: isDev ? true : false,
      show: false,
      opacity: 0.9,
      webPreferences: {
        nodeIntegration: true,
        // ideally would like to use contextIsolation but right now this should work
        contextIsolation: false,
      },
    });

    this.loadFile(file);

    if (isDev) {
      this.webContents.openDevTools();
    }
  }
}

module.exports = MainWindow;

Getting this error

If I move the listeners into the constructor it works,

        this.on('click', () => {
            if (this.mainWindow.isVisible() === true) {
                this.mainWindow.hide();
            } else {
                this.mainWindow.show();
            }
        });

        this.on('right-click', () => {
            const contextMenu = Menu.buildFromTemplate([
                {
                    label: 'Quit',
                    click: () => {
                        app.isQuitting = true;
                        app.quit();
                    },
                },
            ]);

            this.popUpContextMenu(contextMenu);
        });