View file modules/registration/templates/registration_closed.phtml
<?php $this->layout( 'system::layout/default', [ 'title' => __('Registration'), 'page_title' => __('Registration'), ] ) ?> <?= $this->fetch( 'system::app/alert', [ 'alert_type' => 'alert-info', 'alert' => __('Registration is temporarily closed'), ] ) ?>