Drupal's link field is quite generic. You can both add internal paths as external links. Here is how get the correct values in twig.

Solution

{% if content.field_cta %}
  <a href="{{ content.field_cta.0['#url'].toString() }}" class="btn-secondary">{{ node.field_cta.title }}</a>
{% endif %}
// If you are doing this inside a paragraph, use paragraph instead of node

 

 

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