Adding template suggestions for view modes and content types in Drupal 8

mytheme.theme.php

<?php
/**
 * Implements hook_theme_suggestions_HOOK_alter() for node.html.twig.
 */
function MYTHEME_theme_suggestions_node_alter(array &$suggestions, array $variables) {
  // Add template suggestions based on the current view mode.
  $node = $variables['elements']['#node'];
  $suggestions[] = 'node__' . $variables['elements']['#view_mode'];
  $suggestions[] = 'node__' . $node->bundle() . '__' . $variables['elements']['#view_mode'];
}