diff --git a/airflow-core/newsfragments/66564.bugfix.rst b/airflow-core/newsfragments/66564.bugfix.rst
new file mode 100644
index 0000000000000..c18c56e3c2491
--- /dev/null
+++ b/airflow-core/newsfragments/66564.bugfix.rst
@@ -0,0 +1 @@
+Fix deserialization of operators that store ``NOTSET`` (an ``ArgNotSet`` sentinel) on a serialized field. ``OperatorSerialization._deserialize_field_value`` now restores the ``NOTSET`` singleton for any field encoded as ``{__type: ARG_NOT_SET}`` instead of returning the raw encoding dict (or raising for ``_date``-suffixed fields). The user-visible repro is ``TriggerDagRunOperator(logical_date=NOTSET)`` which previously failed to round-trip through ``SerializedDAG``.
diff --git a/airflow-core/src/airflow/serialization/serialized_objects.py b/airflow-core/src/airflow/serialization/serialized_objects.py
index cf0e2dc149f02..fcdc6119454f4 100644
--- a/airflow-core/src/airflow/serialization/serialized_objects.py
+++ b/airflow-core/src/airflow/serialization/serialized_objects.py
@@ -1575,6 +1575,20 @@ def _deserialize_field_value(cls, field_name: str, value: Any) -> Any:
         :param value: The value to deserialize
         :return: The deserialized value
         """
+        # Restore the ``NOTSET`` singleton for any field whose value was serialized as
+        # the generic ARG_NOT_SET encoding. This is checked before the field-name
+        # dispatch so the behavior is symmetric with how ARG_NOT_SET is emitted by
+        # the serializer (a generic encoding, not tied to any field type) and so
+        # any future operator that stores ``NOTSET`` on a non-date field also
+        # round-trips correctly. Without this, deserializing operators such as
+        # ``TriggerDagRunOperator`` (whose ``logical_date`` defaults to ``NOTSET``)
+        # would either fail in ``_deserialize_datetime`` or return the raw encoding
+        # dict from the catch-all branch.
+        if isinstance(value, dict) and value.get(Encoding.TYPE) == DAT.ARG_NOT_SET:
+            from airflow.serialization.definitions.notset import NOTSET
+
+            return NOTSET
+
         if field_name == "downstream_task_ids":
             return set(value) if value is not None else set()
         elif field_name in _HAS_CALLBACK_FIELDS:
diff --git a/airflow-core/tests/unit/serialization/test_serialized_objects.py b/airflow-core/tests/unit/serialization/test_serialized_objects.py
index e672e93cd2313..fbc499b2e6f72 100644
--- a/airflow-core/tests/unit/serialization/test_serialized_objects.py
+++ b/airflow-core/tests/unit/serialization/test_serialized_objects.py
@@ -1011,6 +1011,51 @@ def test_deserialize_datetime_with_timestamp(self):
         assert isinstance(result, datetime)
         assert result.timestamp() == timestamp
 
+    @pytest.mark.parametrize(
+        "field_name",
+        ["logical_date", "start_date", "end_date", "trigger_dag_id", "any_other_field"],
+    )
+    def test_deserialize_field_value_with_arg_not_set(self, field_name):
+        """``_deserialize_field_value`` returns ``NOTSET`` for any ARG_NOT_SET-encoded field.
+
+        Operators may store ``NOTSET`` (an ``ArgNotSet`` instance) on a field to mean
+        "use the default at runtime". When the field is round-tripped through
+        serialization the value is encoded as ``{Encoding.TYPE: DAT.ARG_NOT_SET}``
+        regardless of field type, so ``_deserialize_field_value`` must restore the
+        ``NOTSET`` singleton irrespective of the field name (covers the date-typed
+        case demonstrated by ``TriggerDagRunOperator.logical_date`` and the
+        non-date case for any future operator that uses ``NOTSET`` as a sentinel).
+        """
+        from airflow.serialization.definitions.notset import NOTSET
+        from airflow.serialization.serialized_objects import OperatorSerialization
+
+        value = {Encoding.TYPE: DAT.ARG_NOT_SET}
+        assert OperatorSerialization._deserialize_field_value(field_name, value) is NOTSET
+
+    def test_serialize_deserialize_trigger_dag_run_with_notset_logical_date(self):
+        """End-to-end round trip: serialize ``TriggerDagRunOperator(logical_date=NOTSET)``
+        and confirm the deserialized task carries the ``NOTSET`` singleton on
+        ``logical_date``.
+
+        This pins the symmetry between the serializer (which emits
+        ``{Encoding.TYPE: DAT.ARG_NOT_SET}`` for ``NOTSET`` values) and the
+        deserializer fix in ``_deserialize_field_value``. Without the fix, the
+        deserializer would raise (or return the raw encoding dict) and this test
+        would fail.
+        """
+        from airflow.providers.standard.operators.trigger_dagrun import TriggerDagRunOperator
+        from airflow.serialization.definitions.notset import NOTSET
+        from airflow.serialization.serialized_objects import DagSerialization
+
+        with DAG(DAG_ID, start_date=DEFAULT_DATE) as dag:
+            TriggerDagRunOperator(task_id="test_trigger", trigger_dag_id="downstream_dag")
+
+        serialized = DagSerialization.serialize_dag(dag)
+        deserialized = DagSerialization.deserialize_dag(serialized)
+
+        task = deserialized.task_dict["test_trigger"]
+        assert task.logical_date is NOTSET
+
 
 class TestRetryPolicySerialization:
     """Test that retry_policy is serialized as a boolean flag (has_retry_policy)."""