Is it possible to add to cart with a radio input rather than a select?
The name for your input needs to be purchasableId:

{% for digitalProduct in entry.exampleProducts.all() %}
  &lt;li&gt;
    &lt;div&gt;
      &lt;input 
        type="radio"
        name="purchasableId"
        value="{{digitalProduct.purchasableId}}" /&gt;
    &lt;/div&gt;
  &lt;/li&gt;
{% endfor %}