Add Schema.org BreadcrumbList inline in Drupal 8+ in your theme's templates.

breadcrumb.html.twig

{#
/**
 * @file
 * Theme override for a breadcrumb trail.
 *
 * Available variables:
 * - breadcrumb: Breadcrumb trail items.
 */
#}
{% if breadcrumb %}
  <ol itemscope itemtype="http://schema.org/BreadcrumbList" class="breadcrumbs" aria-label="breadcrumb">
  {% for item in breadcrumb %}
    <li itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem">
      {% if item.url %}
        <a itemprop="item" href="{{ item.url }}">
          <span itemprop="name">{{ item.text }}</span>
          <meta itemprop="position" content="{{ loop.index }}" />
        </a>
      {% else %}
        <span itemprop="item">
          <span itemscope itemprop="identifier" itemtype="http://schema.org/PropertyValue" hidden>
           <meta itemprop="url">{{ url('<current>') }}</span>
          </span>
          <span itemprop="name">{{ item.text }}</span>
          <meta itemprop="position" content="{{ loop.index }}" />
        </span>
      {% endif %}
    </li>
  {% endfor %}
  </ol>
{% endif %}