Are parameters ref or reactive in Vue 3 composition API?

Actually ref does not creates a shallow copy, once you pass an obj to a ref, it will call the createReactiveObject method to generate a reactive object. Regarding shallow ref, you can use the shallowref method, https://v3.vuejs.org/api/refs-api.html#shallowref

Since you have not provide any code, here just give you a simple example for your reference:

Define comments as a reactive object, child no need to ref for the props:

Parent component:

<template>
  <Comment v-for="comment in comments" :comment="comment" :key="comment.id"></Comment>
  <button @click="addCmt">addCmt</button>
</template>

<script>
import Comment from "./components/Comment";
import {reactive} from "vue";
export default {
  name: "Params",
  setup() {
    const comments = reactive([{id: 1, name: 'a'}, {id: 6, name: 'c'}]);
    function addCmt() {
      comments.unshift({id: comments.length + 10, name: 'k'});
    }
    return {
      comments,
      addCmt
    }
  },
  components: {Comment}
}
</script>

Comment component:

<template>
  <div>comments {{ comment.id }}</div>
</template>

<script>
export default {
  name: "Comment",
  props: ['comment'],
  setup(props, ctx) {
    const comment = props.comment;
    return {comment};
  }
}
</script>