Custom Post Type Categories URL not displaying posts

You are specifying the same slug of destinations for both your custom post type and for your taxonomy, unfortunately by default this doesn’t behave how you’d expect due to WordPress’ rewrite API. Which caters for the default nature of posts, archives, taxonomies, slugs and the WordPress template hierarchy.

If this URL structure is not important to you then you could change one of your slugs to destinations and the other to destination. Ensuring you flush your rewrite rules after doing so

Alternatively if this URL structure is important you may find this answer useful