MODULE_form_user_login_form_alter

MODULE_form_user_login_form_alter.module

<?php

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Url;
use Drupal\Component\Render\FormattableMarkup;

/**
 * Implements hook_form_BASE_FORM_ID_alter().
 */
function MODULE_form_user_login_form_alter(&$form, FormStateInterface $form_state, $form_id) {

  $url = Url::fromRoute('user.register');
  $form['register_link'] = [
    '#markup' => new FormattableMarkup('@question <a href="@link">@link_text</a>', [
      '@question' => t('No account?'),
      '@link' => $url->toString(),
      '@link_text' => t('registration'),
    ])
  ];
}