放在App.vue里，似乎是不对的

<template>
  <title>陈尼克</title>

  <div id="app" v-cloak>
  <p>姓名: {{ name }}</p>
  <p>职业: {{ state.work }}</p>
  </div>
</template>

<script>
const { createApp, ref, reactive } = Vue;
const app = {
  setup() {
    const name = ref("Nick")
    const state = reactive({
      work: "前端工程师",
    });
    return {
      state,
      name,
    };
  },
};
</script>

<style>
#app {
  font-family: Avenir, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>

放在index.html里吗？试一试