code: private function writeHyperlinks(XMLWriter $objWriter, PhpspreadsheetWorksheet $pSheet)
      {
          // Hyperlink collection
          $hyperlinkCollection = $pSheet->getHyperlinkCollection();
  
          // Relation ID
          $relationId = 1;
  
          // Write hyperlinks?
          if (!empty($hyperlinkCollection)) {
              $objWriter->startElement('hyperlinks');
  
              foreach ($hyperlinkCollection as $coordinate => $hyperlink) {
                  $objWriter->startElement('hyperlink');
  
                  $objWriter->writeAttribute('ref', $coordinate);
                  if (!$hyperlink->isInternal()) {
                      $objWriter->writeAttribute('r:id', 'rId_hyperlink_' . $relationId);
                      ++$relationId;
                  } else {
                      $objWriter->writeAttribute('location', str_replace('sheet://', '', $hyperlink->getUrl()));
                  }
  
                  if ($hyperlink->getTooltip() != '') {
                      $objWriter->writeAttribute('tooltip', $hyperlink->getTooltip());
                  }
  
                  $objWriter->endElement();
              }
  
              $objWriter->endElement();
          }
      }
docs: Write Hyperlinks.
  
  @param XMLWriter $objWriter XML Writer
  @param PhpspreadsheetWorksheet $pSheet Worksheet