{{ node.title.value }}
{{ content.field_text }}
{{ drupal_view('mysection', 'block_1') }}
{{ drupal_block('mytheme_breadcrumbs') }}

{% include '@mytheme/includes/section.html.twig' %}

node--page.html.twig

region--myregion.html.twig

block--entityviewcontent.html.twig

cache: false
debug: true

<!-- THEME DEBUG -->
<!-- THEME HOOK: 'block' -->
<!-- FILE NAME SUGGESTIONS:
   * block--block-name.html.twig
   * block--block-content--b436f9c6-34ae-4879-8b55-068015a999d3.html.twig
   * block--block-content--bundle-name.html.twig
   * block--block-content.html.twig
   * block--block-content.html.twig
   x block.html.twig
-->
<!-- BEGIN OUTPUT from 'themes/bootstrap/templates/block/block--system.html.twig' -->

{% if nid %}
    nid:{{nid}} <br/>
    title:{{node_title}} <br/>
    body:{{body}}<br/>
    text:{{field_text}} <br/>
{% endif %}

function THEMENAME_preprocess_block(&$vars){
    $node = Drupal::routeMatch()->getParameter('node');
    if ($node instanceof DrupalnodeNodeInterface) {
      // You can get nid and anything else you need from the node object.
      $vars["nid"] = $node->id();
      $vars["node_title"] = $node->getTitle();
      $vars["body"] = $node->body->value;
      $vars["field_text"] = $node->field_text->value;

      //following did not work ?!
      //$vars["field_text"] = $node->get('field_text')->getValue();
      //$vars["field_text"] = $node->field_text->getValue();
    }
}