Electron 9.0.0, unable to install dev tools

Describe the bug After upgrading to electron 9.0.0, the following error is thrown.

(node:63292) ExtensionLoadWarning: Warnings loading extension at /Users/mimimi/Library/Application Support/PROJECTNAME/extensions/nhdogjmejiglipccpnnnanhbledajbpd: Unrecognized manifest key 'browser_action'. Unrecognized manifest key 'update_url'. Permission 'contextMenus' is unknown or URL pattern is malformed. Cannot load extension with file or directory name _metadata. Filenames starting with "_" are reserved for use by the system.
(node:63292) ExtensionLoadWarning: Warnings loading extension at /Users/mimimi/Library/Application Support/PROJECTNAME/extensions/nhdogjmejiglipccpnnnanhbledajbpd: Unrecognized manifest key 'browser_action'. Unrecognized manifest key 'update_url'. Permission 'contextMenus' is unknown or URL pattern is malformed. Cannot load extension with file or directory name _metadata. Filenames starting with "_" are reserved for use by the system.

To Reproduce Init a project and upgrade electron to 9.0.0

Expected behavior The dev tool should be working

Environment (please complete the following information):

• OS and version: macOS 10.15.5
• node version: v12.13.1
• npm version:
• yarn version (if used): 1.22.0
• vue-cli-plugin-electron-builder version : commit f0c7709
• electron version: 9.0.0
• other vue plugins used: vuetify
• custom config for vcp-electron-builder: none
• (if possible) link to your repo: none

[azeranex]

Vue Dev tool is actually working but you have to close and re-open dev tool.

I use following code to make it work from start:

async function createWindow () {
// ...
  if (process.env.WEBPACK_DEV_SERVER_URL) {
    // Load the url of the dev server if in development mode
    await win.loadURL(process.env.WEBPACK_DEV_SERVER_URL)
    if (!process.env.IS_TEST) win.webContents.openDevTools()
// ...

[Al-Rozhkov]

Doesn’t work for me. Additional error message: 'BrowserWindow.addDevToolsExtension' is deprecated and will be removed. Please use 'session.loadExtension' instead.

Permission 'contextMenus' is unknown or URL pattern is malformed. Cannot load extension with file or directory name _metadata. Filenames starting with "_" are reserved for use by the system.