diff -r 34716fd837a4 -r be944660c56a wp/wp-includes/class-wp-feed-cache.php
--- a/wp/wp-includes/class-wp-feed-cache.php	Tue Dec 15 15:52:01 2020 +0100
+++ b/wp/wp-includes/class-wp-feed-cache.php	Wed Sep 21 18:19:35 2022 +0200
@@ -5,8 +5,16 @@
  * @package WordPress
  * @subpackage Feed
  * @since 4.7.0
+ * @deprecated 5.6.0
  */
 
+_deprecated_file(
+	basename( __FILE__ ),
+	'5.6.0',
+	'',
+	__( 'This file is only loaded for backward compatibility with SimplePie 1.2.x. Please consider switching to a recent SimplePie version.' )
+);
+
 /**
  * Core class used to implement a feed cache.
  *