Conditionally Redirect in WordPress with full knowledge of the queried content: https://silvanhagen.com/writing/conditionally-redirect-in-wordpress/

functions.php

<?php
/**
 * Redirect job ads to their parent page if they are not published.
 *
 * @link https://developer.wordpress.org/reference/hooks/template_redirect/
 * @link https://developer.wordpress.org/reference/functions/is_404/
 * @link https://developer.wordpress.org/reference/functions/get_queried_object_id/
 * @link https://developer.wordpress.org/reference/functions/get_post_meta/
 * @link https://developer.wordpress.org/reference/functions/get_post_status/
 * @link https://developer.wordpress.org/reference/functions/wp_get_post_parent_id/
 * @link https://developer.wordpress.org/reference/functions/get_permalink/
 * @link https://developer.wordpress.org/reference/functions/wp_redirect/
 */
add_action('template_redirect', function() {
    if ( is_404() ) {
        global $wp_query;

        // Get the current page ID
        $page_id = $wp_query->get_queried_object_id();

        // Check if the current page has the meta field `is_job_ad`
        $is_job_ad = get_post_meta( $page_id, 'is_job_ad', true );

        // If it's a job ad and the post status is not 'publish'
        if ( $is_job_ad && get_post_status($page_id) !== 'publish' ) {
            // Get the parent page ID
            $parent_id = wp_get_post_parent_id( $page_id );

            // If there is a parent page, get its URL
            if ( $parent_id ) {
                $parent_url = get_permalink( $parent_id );

                // 302 Redirect to the parent page URL
                wp_redirect( $parent_url );
                exit;
            }
        }
    }
});