geo-coop/web/themes/custom/geofresco/geofresco.theme

<?php

/**
 * Preprocess functions for GEO site.
 */
function geofresco_preprocess_page_title(&$variables) {
  // WE SHALL BE SHAMELESS.
  if (!isset($variables['title']) || !is_array($variables['title'])) {
    // The pages we're interested in have title as markup, so bail if it's not.
    return;
  }
  $string = isset($variables['title']['#markup']) ? $variables['title']['#markup'] : FALSE;
  if ($string && $pos = strpos($string, "'s blog", -7)) {
    $uid = substr($string, 0, $pos);
    if (is_numeric($uid) && $account = \Drupal\user\Entity\User::load($uid)) {
      $variables['title'] = [
        '#markup' => t("@username's blog",
          ['@username' => $account->getDisplayName()])
      ];
    }
  }
}