Show Free Gift Option on Cart Template in Shopify

Paste this below code in Shopify > Section > New Section > enter any name of your choice-

{% assign section_collection = section.settings.collection %}
{% unless cart.item_count == 0 %}
  {% assign product_collection_qty = 0 %}
  {% for line_item in cart.items %}
    {% for line_item_product_collection in line_item.product.collections %}
      {% if line_item_product_collection.title == section_collection.title %}
        {% assign product_collection_qty = product_collection_qty | plus: line_item.quantity %}
        {% if product_collection_qty >= 3 %}
          {% assign show_gifting_product = true %}
        {% endif %}
      {% endif %}
    {% endfor %}

    {% if show_gifting_product %}
      <div class="wrapper page-margin">
        <h2 class="free-gift-title">Choose Free Gift of your choice</h2>
        <div class="cart-gift-flex">
          {% for product in section_collection.products %}
            <div class="cart-gift-flex-item">
              <a href="{{ product.url }}"><img src="{{ product.featured_image | img_url: "medium" }}"></a>
              <h3 class="h5--accent strong name_wrapper" style="text-align: center">{{ product.title }}</h3>
              <p style="text-align: center;">{{ product.price | money }}</p>

              <form method="post" action="/cart/add" style="text-align: center">
                <input type="hidden" name="id" value="{{ product.variants.first.id }}">

                <!-- <input min="1" type="number" id="quantity" name="quantity" value="1"/> -->

                <input type="submit" value="ADD TO CART" class="btn">
              </form>
            </div>
          {% endfor %}
        </div>
      </div>
    {% endif %}
  {% endfor %}
{% endunless %}

{% schema %}
{
  "name": "Cart Free Gift",
  "settings": [
    {
      "type": "collection",
      "id": "collection",
      "label": "Select Free Gift Collection"
    }
  ]
}
{% endschema %}


Add this section in your cart-template.liquid file.

Make sure for automatic discount you have to create automatic BOGO discount in Shopify.