How do I change the following code so that it works under PHP 8?

        <?php
        class themeslug_walker_nav_menu extends Walker_Nav_Menu {
          // add classes to ul sub-menus
          function start_lvl( & $output, $depth = 0, $args = array() ) {
            // depth dependent classes
            $indent = ( $depth > 0 ? str_repeat( "\t", $depth ) : '' ); // code indent
            $display_depth = ( $depth + 1 ); // because it counts the first submenu as 0
            $classes = array(
              'sub-menu',
              ( $display_depth % 2 ? 'menu-odd' : 'menu-even' ),
              ( $display_depth >= 2 ? 'sub-sub-menu' : '' ),
              'menu-depth-' . $display_depth
            );
            $class_names = implode( ' ', $classes );

            // build html
            $output .= "\n" . $indent . '<ul class="children">' . "\n";
          }

          // add main/sub classes to li's and links

          function start_el( & $output, $item, $depth = 0, $args = array() ) {
            global $wp_query;
            $indent = ( $depth > 0 ? str_repeat( "\t", $depth ) : '' ); // code indent

            // depth dependent classes
            $depth_classes = array(
              ( $depth == 0 ? 'main-menu-item' : 'sub-menu-item' ),
              ( $depth >= 2 ? 'sub-sub-menu-item' : '' ),
              ( $depth % 2 ? 'menu-item-odd' : 'menu-item-even' ),
              'menu-item-depth-' . $depth
            );
            $depth_class_names = esc_attr( implode( ' ', $depth_classes ) );

            // passed classes
            $classes = empty( $item->classes ) ? array() : ( array )$item->classes;
            $class_names = esc_attr( implode( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) ) );


            // build html
            $output .= $indent . '<li class="' . "more-nav " . $class_names . '">';

            // link attributes
            $attributes = !empty( $item->attr_title ) ? ' title="' . esc_attr( $item->attr_title ) . '"': '';
            $attributes .= !empty( $item->target ) ? ' target="' . esc_attr( $item->target ) . '"': '';
            $attributes .= !empty( $item->xfn ) ? ' rel="' . esc_attr( $item->xfn ) . '"': '';
            $attributes .= !empty( $item->url ) ? ' href="' . esc_attr( $item->url ) . '"': '';
            $attributes .= ' class=""';

            if ( $depth > 0 )$format="<a%2$s><div class="sub">%3$s%4$s%5$s</div></a>%6$s";

            $item_output = sprintf( $format,
              $args->before,
              $attributes,
              $args->link_before,
              apply_filters( 'the_title', $item->title, $item->ID ),
              $args->link_after,
              $args->after
            );

            // build html
            $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );

          }
        }

        ?>
        <?php wp_nav_menu( array( 'container' => 'false', 'menu_class' => '', 'items_wrap' => '%3$s', 'theme_location' => 'top', 'walker' => new themeslug_walker_nav_menu ) ); ?>
        <?php if ( ( twentyseventeen_is_frontpage() || ( is_home() && is_front_page() ) ) && has_custom_header() ) : ?>
        <a href="#content" class="menu-scroll-down"><?php echo twentyseventeen_get_svg( array( 'icon' => 'arrow-right' ) ); ?><span class="screen-reader-text">
        <?php _e( 'Scroll down to content', 'twentyseventeen' ); ?>
        </span></a>
        <?php endif; ?>

I would be grateful for tips

Greetings
Morrow