--- a/wp/wp-includes/widgets/class-wp-widget-calendar.php	Tue Dec 15 15:52:01 2020 +0100
+++ b/wp/wp-includes/widgets/class-wp-widget-calendar.php	Wed Sep 21 18:19:35 2022 +0200
@@ -33,6 +33,7 @@
 			'classname'                   => 'widget_calendar',
 			'description'                 => __( 'A calendar of your site’s posts.' ),
 			'customize_selective_refresh' => true,
+			'show_instance_in_rest'       => true,
 		);
 		parent::__construct( 'calendar', __( 'Calendar' ), $widget_ops );
 	}