Vite entry-legacy.js is not ES5 compatible

Environment

• Operating System: Darwin
• Node Version: v16.13.0
• Nuxt Version: 2.16.0-27358576.777a4b7f
• Package Manager: pnpm@6.32.4
• Builder: vite
• User Config: bridge, hooks, buildModules
• Runtime Modules: -
• Build Modules: @nuxt/bridge@3.0.0-27530716.c4f8671

Reproduction

Create empty project with this nuxt.config.js:

import { defineNuxtConfig } from '@nuxt/bridge'
import legacy from '@vitejs/plugin-legacy'

export default defineNuxtConfig({
  bridge: {
    vite: true,
  },
  hooks: {
    'vite:extendConfig': config => {
      config.plugins.forEach((plugin, i) => {
        if (Array.isArray(plugin) && plugin[0].name === 'vite:legacy-config') {
          config.plugins[i] = legacy({
            targets: ['ie 9'],
          })
        }
      })
    },
  },
})

Then run nuxi build.

.output/public/_nuxt/entry-legacy.c81f3a42.js will include code that does not run in IE 9:

var appConfig = window?.__NUXT__?.config.app || {}

Describe the bug

nuxi build generates ES5-incompatible javascript even if @vitejs/plugin-legacy is configured with IE 9 target. The plugin itself works fine, the problem is apparently that Nuxt-injected code is not processed with that plugin.

Additional context

No response

Logs

No response

Start with the Vite integration involved in the vite:extendConfig hook and trace how Nuxt-injected code reaches .output/public/_nuxt/entry-legacy.c81f3a42.js. Run nuxi build using the reported configuration and inspect the generated legacy entry. Done means the Nuxt-injected output is processed for the configured IE 9 target and no optional-chaining syntax remains.