--- a/Model/App/Response/HttpPlugin.php
+++ b/Model/App/Response/HttpPlugin.php	(date 1762332952396)
@@ -41,9 +41,13 @@
             return;
         }
 
+        /*
+         * ADDED BY PATCH: $varyCookie !== null
+         * Without this varnish will never get a cacheable response from Magento, because Varnish does not know a Vary-Key, and will never send any
+         */
         $currentVary = $this->context->getVaryString();
         $varyCookie = $this->request->get(HttpResponse::COOKIE_VARY_STRING);
-        if ($currentVary !== $varyCookie) {
+        if ($varyCookie !== null && $currentVary !== $varyCookie) {
             //prevent caching with the old vary cookie
             $subject->setNoCacheHeaders();
         }