<b-card no-body class="mb-1" v-for="n in 10">
  <b-card-header header-tag="header" role="tab">
    <b-btn block href="#" v-b-toggle.accordion[how to render n here??]>
      Category
    </b-btn>
  </b-card-header>
  <b-collapse :id="`accordion${n}`" accordion="my-accordion" role="tabpanel">
    <b-card-body>
      <b-list-group>
        <b-list-group-item href="#">
          Sub-category (100)
        </b-list-group-item>
        <b-list-group-item href="#">
          Sub-category (100)
        </b-list-group-item>
      </b-list-group>
    </b-card-body>
  </b-collapse>
</b-card>