Issue #2987060 by Sut3kh, andypost, greggles, Anybody, lkacenja, jnrfred:...

<?php

namespace Drupal\email_registration\Plugin\Commerce\CheckoutPane;

use Drupal\commerce_checkout\Plugin\Commerce\CheckoutPane\CompletionRegister;

use Drupal\Core\Form\FormStateInterface;

/**

 * Provides the registration pane without username.

 *

 * Assumes email_registration is enabled.

 *

 * @CommerceCheckoutPane(

 *   id = "email_registration_completion_registration",

 *   label = @Translation("Email registration guest registration after checkout"),

 * )

 */

class EmailRegistrationCompletionRegistration extends CompletionRegister {

  /**

   * {@inheritdoc}

   */

  public function buildPaneForm(array $pane_form, FormStateInterface $form_state, array &$complete_form) {

    $pane_form = parent::buildPaneForm($pane_form, $form_state, $complete_form);

    // Set the name as per email_registration_form_user_register_form_alter().

    $pane_form['name'] = [

      '#type' => 'hidden',

      '#value' => 'email_registration_' . user_password(),

    ];

    // Try and help password managers.

    // https://www.chromium.org/developers/design-documents/form-styles-that-chromium-understands

    $pane_form['email'] = [

      '#type' => 'textfield',

      '#value' => $this->order->getEmail(),

      '#attributes' => [

        'autocomplete' => 'username',

      ],

      '#wrapper_attributes' => [

        'style' => 'display: none;',

      ],

    ];

    return $pane_form;

  }

}