How to use :not() in tailwind.css

The answer is in the link to last in the docs, that you shared.

Just add last:border-b-0 to all list items, and it will remove the border-bottom if it is the last-child.

<ul>
  <li
    v-for="(item, index) in items"
    :key="`item-${index}`"
    class="border-solid border-b border-black last:border-b-0"
  >
    Item
  </li>
</ul>