cl-deck-builder2/templates/builder/saved-category-list.html

<div class="select">
  <select hx-get="/builder/decks-by-cat-id"
          hx-params="id"
          hx-target="#saved-deck-list"
          hx-trigger="change"
          name="id">
    <option value="">Category</option>
    {% for category in categories %}
    <option value="{{ category.id }}"{% if category.id == id %} selected{% endif %}>{{ category.name }}</option>
    {% endfor %}
  </select>
</div>