messages from local i18n block not found by vue-i18n

Question

I have an older project built with vue2 where I use vue-i18n with the custom <i18n> blocks for component-local translations. I wanted to test how that would work with vue3. I created a new project with vue3 + vuetify 3 + vue-i18n 9 and I cannot make the local <i18n> block work.

I reduced the code to the following:

vite.config.js

// Plugins
import vue from "@vitejs/plugin-vue";
import vuetify, { transformAssetUrls } from "vite-plugin-vuetify";
import ViteFonts from "unplugin-fonts/vite";

// Utilities
import { defineConfig } from "vite";
import { fileURLToPath, URL } from "node:url";

import VueI18nPlugin from "@intlify/unplugin-vue-i18n/vite";

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [
    vue({
      template: { transformAssetUrls },
    }),
    // https://github.com/vuetifyjs/vuetify-loader/tree/next/packages/vite-plugin
    vuetify({
      autoImport: true,
      styles: {
        configFile: "src/styles/settings.scss",
      },
    }),
    ViteFonts({
      google: {
        families: [
          {
            name: "Roboto",
            styles: "wght@100;300;400;500;700;900",
          },
        ],
      },
    }),
    VueI18nPlugin({}),
  ],
  define: { "process.env": {} },
  resolve: {
    alias: {
      "@": fileURLToPath(new URL("./src", import.meta.url)),
    },
    extensions: [".js", ".json", ".jsx", ".mjs", ".ts", ".tsx", ".vue"],
  },
  server: {
    port: 3000,
  },
});

main.js

import App from "./App.vue";

let messages = {
  en: {
    example: "Whatever in main.js",
  },
};

// Composables
import { createApp } from "vue";
import { createI18n } from "vue-i18n";

const i18n = createI18n({
  locale: "en",
  messages,
});

const app = createApp(App);
app.use(i18n).mount("#app");

App.vue

<i18n>
{"en": {"test": "FOO"}}
</i18n>

<template>
  <h1>{{ $t("test") }}</h1>
  <h2>{{ $t("example") }}</h2>
</template>

The output is:

So, the messages defined when initializing i18n in main.js is used, but the one from the local block is not. Even though it matches the docs. What am I missing?