function update_modified_date_on_publish($new_status, $old_status, $post) {
    // Only update if transitioning from 'future' (scheduled) to 'publish'
    if ($old_status === 'future' && $new_status === 'publish') {
        // Update the post's modified date to match the published date
        wp_update_post(array(
            'ID'            => $post->ID,
            'post_modified' => current_time('mysql'),
            'post_modified_gmt' => current_time('mysql', 1),
        ));
    }
}

add_action('transition_post_status', 'update_modified_date_on_publish', 10, 3);