diff -u b/core/modules/system/src/Theme/DbUpdateNegotiator.php b/core/modules/system/src/Theme/DbUpdateNegotiator.php
--- b/core/modules/system/src/Theme/DbUpdateNegotiator.php
+++ b/core/modules/system/src/Theme/DbUpdateNegotiator.php
@@ -32,15 +32,11 @@
    *
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
    *   The config factory.
-   * @param \Drupal\Core\Extension\ThemeHandlerInterface|null $theme_handler
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
    *   The theme handler.
    */
-  public function __construct(ConfigFactoryInterface $config_factory, ThemeHandlerInterface $theme_handler = NULL) {
+  public function __construct(ConfigFactoryInterface $config_factory, ThemeHandlerInterface $theme_handler) {
     $this->configFactory = $config_factory;
-    if ($theme_handler === NULL) {
-      @trigger_error('Calling ' . __METHOD__ . '() without the $theme_handler argument is deprecated in drupal:9.4.0 and $theme_handler argument will be required in drupal:10.0.0. See https://www.drupal.org/node/TBD', E_USER_DEPRECATED);
-      $theme_handler = \Drupal::service('theme_handler');
-    }
     $this->themeHandler = $theme_handler;
   }