Custom walker class to display ACF image field to wp_list_pages

CustomWalkerPage

<?php 
class My_Walker_Page extends Walker_Page {
  public function start_el( &$output, $page, $depth = 0, $args = array(), $current_page = 0 ) {
    if ( $depth ) {
      $indent = str_repeat( "\t", $depth );
    } else {
      $indent = '';
    }

    $css_class = array( 'page_item', 'page-item-' . $page->ID );

    if ( isset( $args['pages_with_children'][ $page->ID ] ) ) {
      $css_class[] = 'page_item_has_children';
    }

    if ( ! empty( $current_page ) ) {
      $_current_page = get_post( $current_page );
      if ( $_current_page && in_array( $page->ID, $_current_page->ancestors ) ) {
        $css_class[] = 'current_page_ancestor';
      }
      if ( $page->ID == $current_page ) {
        $css_class[] = 'current_page_item';
      } elseif ( $_current_page && $page->ID == $_current_page->post_parent ) {
        $css_class[] = 'current_page_parent';
      }
    } elseif ( $page->ID == get_option('page_for_posts') ) {
      $css_class[] = 'current_page_parent';
    }

    $css_classes = implode( ' ', apply_filters( 'page_css_class', $css_class, $page, $depth, $args, $current_page ) );

    if ( '' === $page->post_title ) {
      /* translators: %d: ID of a post */
      $page->post_title = sprintf( __( '#%d (no title)' ), $page->ID );
    }

    $args['link_before'] = empty( $args['link_before'] ) ? '' : $args['link_before'];
    $args['link_after'] = empty( $args['link_after'] ) ? '' : $args['link_after'];
    
    /* ACFでフィールドpageimgを設定している想定 */
    $image = get_field( 'pageimg', $page->ID );
    $pageimg = empty( $image ) ? '' : sprintf(
      /* 出力用のマークアップ設定 */
      '<div><img src="%s" alt="%s" /></div>',
      $image['url'],
      $image['alt']
    );
    
    $output .= $indent . sprintf(
      '<li class="%s"><a href="%s">%s%s%s%s</a>',
      $css_classes,
      get_permalink( $page->ID ),
      $pageimg,
      $args['link_before'],
      /** This filter is documented in wp-includes/post-template.php */
      apply_filters( 'the_title', $page->post_title, $page->ID ),
      $args['link_after']
    );

    if ( ! empty( $args['show_date'] ) ) {
      if ( 'modified' == $args['show_date'] ) {
        $time = $page->post_modified;
      } else {
        $time = $page->post_date;
      }

      $date_format = empty( $args['date_format'] ) ? '' : $args['date_format'];
      $output .= " " . mysql2date( $date_format, $time );
    }
  }
}

Original thread
https://ja.wordpress.org/support/topic/wp_list_pagesでカスタムフィールドの値を入れたい%E3%80%82/