This was accidentally left out of commit c050d6a01e (string(TIMESTAMP): add %f specifier for microseconds, 2022-01-27, v3.23.0-rc1~59^2).
@@ -491,6 +491,8 @@ specifiers:
The second of the current minute. 60 represents a leap second. (00-60)
``%f``
+ .. versionadded:: 3.23
+
The microsecond of the current second (000000-999999).
``%U``