Support domain in selection criteria of page manager variant

I'm having the same issue. I'm upgrading a site to Drupal 10, and some of my pages stopped working because they had domain in selection criteria, but now it doesn't appear on D10.

In case it's useful to anyone, I'll add the code for the condition I had to create, which replicates the old one.

<?php

namespace Drupal\custom_module\Plugin\Condition;

use Drupal\Core\Condition\ConditionPluginBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Provides a 'Current Domain' condition.
 *
 * @Condition(
 *   id = "current_domain",
 *   label = @Translation("Current Domain"),
 *   context = {
 *     "url" = @ContextDefinition("any", required = FALSE, label = @Translation("URL"))
 *   }
 * )
 */
class CurrentDomainCondition extends ConditionPluginBase {

  /**
   * {@inheritdoc}
   */
  public function evaluate() {
    if ($this->isNegated()) {
      return !$this->matchDomain();
    }
    return $this->matchDomain();
  }

  /**
   * Checks if the current domain matches one of the configured domains.
   *
   * @return bool
   *   TRUE if the domains match, FALSE otherwise.
   */
  protected function matchDomain() {
    $configured_domains = $this->configuration['domains'] ?? [];
    $domain = \Drupal::service('domain.negotiator')->getActiveId();
    return in_array($domain, $configured_domains);
  }

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
        'domains' => [],
      ] + parent::defaultConfiguration();
  }

  /**
   * {@inheritdoc}
   */
  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
    $all_domains = $this->getAvailableDomains();

    $form['domains'] = [
      '#type' => 'checkboxes',
      '#title' => $this->t('Domains'),
      '#options' => $all_domains,
      '#default_value' => $this->configuration['domains'],
      '#description' => $this->t('Select the domains where this condition should apply.'),
      '#required' => TRUE,
    ];

    return parent::buildConfigurationForm($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
    $selected_domains = array_filter($form_state->getValue('domains'));
    $this->configuration['domains'] = $selected_domains;
    parent::submitConfigurationForm($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function summary() {
    $domains = $this->configuration['domains'] ?? [];
    if (!empty($domains)) {
      return $this->t('The current domain is one of: @domains.', ['@domains' => implode(', ', $domains)]);
    }
    return $this->t('No domains selected.');
  }

  /**
   * Fetch available domains for selection.
   *
   * @return array
   *   An array of available domains as key-value pairs (domain => label).
   */
  protected function getAvailableDomains() {
    $domains = [];
    if (\Drupal::moduleHandler()->moduleExists('domain')) {
      $domain_storage = \Drupal::entityTypeManager()->getStorage('domain');
      $all_domains = $domain_storage->loadMultiple();
      foreach ($all_domains as $domain) {
        // Use the machine name (ID) as the key and the label as the value.
        $machine_name = $domain->id();
        $label = $domain->label();
        $domains[$machine_name] = $label;
      }
    }
    return $domains;
  }

}