A macro which retrieves the top-level parent of the term attached to the current post.

get_ancestor_macro.php

<?php

add_action( 'jet-engine/register-macros', function(){ 

	class Get_Ancestor extends \Jet_Engine_Base_Macros {

		public function macros_tag() {
			return 'get_ancestor';
		}

		public function macros_name() {
			return esc_html__( 'Get Ancestor', 'jet-engine' );
		}

		public function macros_args() {
			return array();
		}
		
		public function macros_callback( $args = array() ) {

				$categories = get_the_terms(get_the_ID(), 'category');
    
				// Check if the post has terms assigned
				if ($categories && !is_wp_error($categories)) {
					// Get the first category assigned to the post
					$category = reset($categories);

					// Get ancestors of the category (parent categories)
					$ancestors = get_ancestors($category->term_id, 'category');

					// If the category has no ancestors, it is a top-level category
					if (empty($ancestors)) {
						// Return the ID of the top-level category
						return $category->term_id;
					} else {
						// Return the ID of the top-level parent category
						return end($ancestors);
					}
				} else {
					// If no terms are assigned, return 0
					return 0;
				}
			}
		
	}
	
	new Get_Ancestor();
	
} );