Electron supports the Pepper Flash plugin. To use the Pepper Flash plugin in Electron, you should manually specify the location of the Pepper Flash plugin and then enable it in your application.
On macOS and Linux, the details of the Pepper Flash plugin can be found by
  navigating to chrome://plugins in the Chrome browser. Its location and version
  are useful for Electron's Pepper Flash support. You can also copy it to another
  location.
You can directly add --ppapi-flash-path and --ppapi-flash-version to the
  Electron command line or by using the app.commandLine.appendSwitch method
  before the app ready event. Also, turn on plugins option of BrowserWindow.
For example:
const {app, BrowserWindow} = require('electron')
  const path = require('path')
  
  // Specify flash path, supposing it is placed in the same directory with main.js.
  let pluginName
  switch (process.platform) {
    case 'win32':
      pluginName = 'pepflashplayer.dll'
      break
    case 'darwin':
      pluginName = 'PepperFlashPlayer.plugin'
      break
    case 'linux':
      pluginName = 'libpepflashplayer.so'
      break
  }
  app.commandLine.appendSwitch('ppapi-flash-path', path.join(__dirname, pluginName))
  
  // Optional: Specify flash version, for example, v17.0.0.169
  app.commandLine.appendSwitch('ppapi-flash-version', '17.0.0.169')
  
  app.on('ready', () => {
    let win = new BrowserWindow({
      width: 800,
      height: 600,
      webPreferences: {
        plugins: true
      }
    })
    win.loadURL(`file://${__dirname}/index.html`)
    // Something else
  })You can also try loading the system wide Pepper Flash plugin instead of shipping
  the plugins yourself, its path can be received by calling
  app.getPath('pepperFlashSystemPlugin').
<webview> TagAdd plugins attribute to <webview> tag.
<webview src="https://www.adobe.com/software/flash/about/" plugins></webview>You can check if Pepper Flash plugin was loaded by inspecting
  navigator.plugins in the console of devtools (although you can't know if the
  plugin's path is correct).
The architecture of Pepper Flash plugin has to match Electron's one. On Windows, a common error is to use 32bit version of Flash plugin against 64bit version of Electron.
On Windows the path passed to --ppapi-flash-path has to use \ as path
  delimiter, using POSIX-style paths will not work.
For some operations, such as streaming media using RTMP, it is necessary to grant wider permissions to players’ .swf files. One way of accomplishing this, is to use nw-flash-trust.