Hi Paul,

This might get a bit tricky, but it is likely possible to some extent via custom code. I have an experimental solution, which hooks into the filters and tries to restrict them to the current possible archive result set.

This is an extract from a possible feature in the upcoming version, but it should do the trick to some extent. Instructions below, but let me know if you need help with it:

function get_available_taxonomy_terms( $taxonomy ) {
	global $wpdb;

	// Initialize terms array
	$terms = [];
	$cache_key = 'terms_' . $taxonomy;

	// Get the current queried object
	$current_queried_object = get_queried_object();

	// Check if we're on a term archive
	if ( is_a( $current_queried_object, 'WP_Term' ) ) {
		// Update cache key to include the term ID
		$cache_key .= '_' . $current_queried_object->term_id;

		// Check transient cache
		$cached_terms = get_transient( $cache_key );
		if ( false !== $cached_terms ) {
			return $cached_terms;
		}

		// Get post IDs in the current category using a custom SQL query
		$query = $wpdb->prepare(
				"
            SELECT DISTINCT tr.object_id
            FROM {$wpdb->term_relationships} tr
            INNER JOIN {$wpdb->term_taxonomy} tt ON tr.term_taxonomy_id = tt.term_taxonomy_id
            WHERE tt.taxonomy = %s
            AND tt.term_id = %d
            ",
				$current_queried_object->taxonomy, // e.g., 'category'
				$current_queried_object->term_id
		);

		$post_ids = $wpdb->get_col( $query );

		if ( empty( $post_ids ) ) {
			return []; // No posts in this category, return empty array
		}

		// Use get_terms() to get terms associated with these post IDs
		$terms = get_terms( [
				'taxonomy'   => $taxonomy,
				'hide_empty' => false, // Include terms even if empty in other contexts
				'object_ids' => $post_ids, // Filter by post IDs
				'fields'     => 'all',
		] );

		if ( is_wp_error( $terms ) ) {
			$terms = [];
		}
	} else {
		// Not a term archive, fall back to all terms for the taxonomy
		$cached_terms = get_transient( $cache_key );
		if ( false !== $cached_terms ) {
			return $cached_terms;
		}

		// Get all terms for the taxonomy
		$terms = get_terms( [
				'taxonomy'   => $taxonomy,
				'hide_empty' => true, // Only include terms with associated posts
				'fields'     => 'all',
		] );

		if ( is_wp_error( $terms ) ) {
			$terms = [];
		}
	}

	// Cache the results for 1 hour
	set_transient( $cache_key, $terms, HOUR_IN_SECONDS );

	return $terms;
}

add_filter('asp_fontend_get_taxonomy_terms', function( $terms, $taxonomy, $args, $needed_all ){
	return get_available_taxonomy_terms($taxonomy);
}, 10, 4);

Try adding this code via the Code Snippets plugin or to the functions.php file in your theme/child theme directory – make sure to have a full server back-up first for safety. For more details you can check the safe coding guidelines.

Great! Thank you very much for the feedback, I will make sure to integrate this to the upcoming release 🙂