ACF Post Object Field Term Filter

functions.php

<?php

/**
 * Filters the query arguments for the 'featured_posts' ACF Post Object field.
 * The filter limits the displayed posts to those associated with the currently edited/viewed term
 * for the taxonomies: 'category', and 'post_tag'.
 *
 * @param array $args   The WP_Query arguments.
 * @param array $field  The field settings.
 * @param int   $post_id The post ID (or term ID, depending on context).
 * 
 * @return array Modified query arguments.
 */
function sjd_filter_post_object_query( $args, $field, $post_id ) {
	// Check if this is the specific field we want to modify.
	if ( 'featured_posts' === $field['name'] ) {
		
		// Check if it's a term ID and extract the ID.
		if ( strpos( $post_id, 'term_' ) === 0 ) {
			$term_id = str_replace( 'term_', '', $post_id );
			$term = get_term( $term_id );

			// Check if term belongs to the specified taxonomies.
			if ( $term instanceof WP_Term && in_array( $term->taxonomy, [ 'category', 'post_tag' ], true ) ) {
				$args['tax_query'] = [
					[
						'taxonomy' => $term->taxonomy,
						'field'    => 'term_id',
						'terms'    => $term->term_id,
						'operator' => 'IN',
					],
				];
			}
		}
	}

	return $args;
}
add_filter( 'acf/fields/post_object/query', 'sjd_filter_post_object_query', 10, 3 );