function MYMODULE_preprocess_node(&$variables) {
  kpr(Drupal::currentUser()->getLastAccessedTime());
}

/**
 * Implements hook_preprocess_HOOK() for node templates.
 */
function mymodule_preprocess_node(&$variables) {
  $variables['content']['timestamp'] = [
    '#lazy_builder' => ['mymodule_timestamp_current_user', []],
    '#create_placeholder' => TRUE,
  ];
}

/**
 * #lazy_builder callback; builds timestamp markup with current user access time.
 */
function mymodule_timestamp_current_user() {
  $timestamp = Drupal::currentUser()->getLastAccessedTime();
  return [
    '#markup' => $timestamp,
    '#cache' => ['max-age' => 0],
  ];
}

use DrupalnodeEntityNodeType;
use DrupalCoreEntityEntityInterface;
use DrupalCoreEntityDisplayEntityViewDisplayInterface;

function MYMODULE_entity_extra_field_info() {

  $extra = [];

  foreach (NodeType::loadMultiple() as $bundle) {

    $extra['node'][$bundle->id()]['display']['last_accessed'] = [
      'label'       => t('Node Last Accessed'),
      'description' => t('Displays the timestamp the current node got last accessed by the current user'),
      'visible'     => FALSE, // Initially set to hidden on Display Settings.
    ];
  }

  return $extra;
}

function MYMODULE_node_view(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display, $view_mode) {

  $current_uid = Drupal::currentUser()->id();
  $current_user = DrupaluserEntityUser::load($current_uid);

  $current_nid = $entity->id();

  // Now you have the current user entity and the current node ID.

  // Now you need to get the value of the custom field which probably should
  // be an associated array of node IDs and timestamps.
  $access_data = $current_user->get('field_node_access_data')->getValue();

  // Now you need to look up if the current node ID already is in it and if so,
  // retrieve its timestamp value.
  $timestamp = ... // your job.

  if ($display->getComponent('last_accessed')) {

    $build['last_accessed'] = [
      '#markup' => $timestamp,
      // I hope this works that way. That the cache gets disabled properly for
      // just this pseudo field.
      '#cache' => ['max-age' => 0],
    ];
  }

  // And now finally after the timestamp has been rendered it needs to get updated.
  $current_user->set('field_node_access_data')->... // Your job. Probably something with time().
  $current_user->save();
}

/**
 * This creates a database to store the last access timestamp per node per user.
 */

/**
 * implements HOOK_preprocess_node().
 */
function node_access_timestamp_by_user_preprocess_node(&$variables) {

  // Set current user ID.
  $uid = Drupal::currentUser()->id();

  // Check if user is authenticated.
  if ($uid != 0) {

    // Get current NID, Timestamp, and DB.
    $currentNID = Drupal::routeMatch()->getRawParameter('node');
    $currentTimestamp = intval(time());
    $database = Drupal::database();

    // Query our DB.
    $queryDBEntries = $database
      ->select('node_access_timestamp_by_user', 'timestamp')
      ->fields('timestamp')
      ->condition('uid', $uid, "=")
      ->condition('nid', $currentNID, "=");

    // Fetch DB data.
    $result = $queryDBEntries->execute()->fetchAll();

    // Check if table row exists and overwrite.
    if ($result[0]->uid == $uid && $result[0]->nid == $currentNID) {
      $database
        ->update('node_access_timestamp_by_user')
        ->fields([
          'timestamp' => $currentTimestamp,
        ])
        ->condition('uid', $uid, '=')
        ->condition('nid', $currentNID, '=')
        ->execute();
    }

    // Check if table row does not exist and create.
    if ($result[0]->uid != $uid && $result[0]->nid != $currentNID) {
      $database
        ->insert('node_access_timestamp_by_user')
        ->fields([
          'uid' => $uid,
          'nid' => $currentNID,
          'timestamp' => $currentTimestamp,
        ])
        ->execute();
    }

    // Set our $variables to print in twig.
    if ($result[0]->nid == $currentNID) {
      $variables['nodeAccessTimestampByUser_uid'] = $result[0]->uid;
      $variables['nodeAccessTimestampByUser_nid'] = $result[0]->nid;
      $variables['nodeAccessTimestampByUser_timestamp'] = $result[0]->timestamp;
    }

  }

}

/**
* Implements HOOK_install().
*
* Creates some default entries on this module custom table.
*
* @see hook_install()
*
* @ingroup node_access_timestamp_by_user
*/
function node_access_timestamp_by_user_install() {

  $currentTimestamp = intval(time());
  $database = Drupal::database();

  // Add a default entry.
  $fields = [
    'uid' => '1',
    'nid' => '1',
    'timestamp' => $currentTimestamp,
  ];
  $database
    ->insert('node_access_timestamp_by_user')
    ->fields($fields)
    ->execute();
}

/**
* Implements HOOK_schema().
*
* Defines the database tables used by this module.
*
* @see hook_schema()
*
* @ingroup node_access_timestamp_by_user
*/
function node_access_timestamp_by_user_schema() {

  $currentTimestamp = intval(time());

  $schema['node_access_timestamp_by_user'] = [
    'description' => 'Stores node access timestamp by user per node.',
    'fields' => [
      'uid' => [
        'type' => 'int',
        'not null' => TRUE,
        'default' => 1,
        'description' => "User's {users}.uid",
    ],
      'nid' => [
        'type' => 'int',
        'not null' => TRUE,
        'default' => 1,
        'description' => "Node ID",
    ],
      'timestamp' => [
        'type' => 'int',
        'not null' => TRUE,
        'default' => $currentTimestamp,
        'description' => "Timestamp",
    ],
    ],
    'primary key' => ['nid'],
    'indexes' => [
      'uid' => ['uid'],
      'nid' => ['nid'],
      'timestamp' => ['timestamp'],
    ],
  ];

  return $schema;
}

<table>
  <tbody>
      <tr>
          <td>UID</td>
          <td>{{ nodeAccessTimestampByUser_uid }}</td>
      </tr>
      <tr>
        <td>NID</td>
        <td>{{ nodeAccessTimestampByUser_nid }}</td>
    </tr>
    <tr>
        <td>Timestamp</td>
        <td>{{ nodeAccessTimestampByUser_timestamp }}</td>
    </tr>
  </tbody>
</table>