Add another limitation

Doc/library/typing.rst

@@ -2446,6 +2446,14 @@ types.
 
       .. versionadded:: 3.9
 
+      .. note::
+
+         If ``from __future__ import annotations`` is used or if annotations
+         are given as strings, annotations are not evaluated when the
+         ``TypedDict`` is defined. Therefore, the runtime introspection that
+         ``__required_keys__`` and ``__optional_keys__`` rely on may not work
+         properly, and the values of the attributes may be incorrect.
+
    See :pep:`589` for more examples and detailed rules of using ``TypedDict``.
 
    .. versionadded:: 3.8