try

lisp/transient.el

@@ -39,6 +39,7 @@
 (require 'eieio)
 (require 'edmacro)
 (require 'format-spec)
+(require 'pcase)
 
 (eval-and-compile
   (when (and (featurep 'seq)
@@ -85,6 +86,13 @@ similar defect.") :emergency))
 (defvar Man-notify-method)
 (defvar pp-default-function) ; since Emacs 29.1
 
+(when (< emacs-major-version 28)
+  (message "-------------------------------backport")
+  (pcase-defmacro cl-type (type)
+    "Pcase pattern that matches objects of TYPE.
+TYPE is a type descriptor as accepted by `cl-typep', which see."
+  `(pred (pcase--flip cl-typep ',type))))
+
 (defmacro transient--with-emergency-exit (id &rest body)
   (declare (indent defun))
   (unless (keywordp id)