The update.post_update_registry has been changed to support themes. See the Themes support post update functions change record for more information.
The following method name changes have been made in order to support this:
\Drupal\Core\Update\UpdateRegistry::getModuleUpdateFunctions()is deprecated in favor of\Drupal\Core\Update\UpdateRegistry::getUpdateFunctions()\Drupal\Core\Update\UpdateRegistry::filterOutInvokedUpdatesByModule()is deprecated in favor of\Drupal\Core\Update\UpdateRegistry::filterOutInvokedUpdatesByExtension()
Additionally, the update.post_update_registry service is no longer directly invoked from the module_installer service. Instead the post update registry subscribes to the config save event and updates its internal list of installed extensions and state storage of existing update functions based on configuration changes.
Note: This feature did not work in 9.4.0-alpha1 for themes that were used for the Drupal installer. It was fixed by #3279850: Theme post updates are not recognised when the theme is used in the installer for the next release.
