diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index aef82392590d3..0811adbeeeda0 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -240,7 +240,7 @@ def _iterate_slices(self) -> Iterable[Series]:
             input="series", examples=_apply_docs["series_examples"]
         )
     )
-    def apply(self, func, *args, **kwargs):
+    def apply(self, func, *args, **kwargs) -> Series:
         return super().apply(func, *args, **kwargs)
 
     @doc(_agg_template, examples=_agg_examples_doc, klass="Series")
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 65e8b238cd476..9886ab53fb9f3 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -924,7 +924,9 @@ def _make_wrapper(self, name: str) -> Callable:
             # as are not passed directly but in the grouper
             f = getattr(self._obj_with_exclusions, name)
             if not isinstance(f, types.MethodType):
-                return self.apply(lambda self: getattr(self, name))
+                #  error: Incompatible return value type
+                # (got "NDFrameT", expected "Callable[..., Any]")  [return-value]
+                return cast(Callable, self.apply(lambda self: getattr(self, name)))
 
         f = getattr(type(self._obj_with_exclusions), name)
         sig = inspect.signature(f)
@@ -1350,7 +1352,7 @@ def _aggregate_with_numba(self, data, func, *args, engine_kwargs=None, **kwargs)
             input="dataframe", examples=_apply_docs["dataframe_examples"]
         )
     )
-    def apply(self, func, *args, **kwargs):
+    def apply(self, func, *args, **kwargs) -> NDFrameT:
 
         func = com.is_builtin_func(func)
 
@@ -1410,7 +1412,7 @@ def _python_apply_general(
         f: Callable,
         data: DataFrame | Series,
         not_indexed_same: bool | None = None,
-    ) -> DataFrame | Series:
+    ) -> NDFrameT:
         """
         Apply function f in python space
 
@@ -1804,7 +1806,7 @@ def all(self, skipna: bool = True):
     @final
     @Substitution(name="groupby")
     @Appender(_common_see_also)
-    def count(self) -> Series | DataFrame:
+    def count(self) -> NDFrameT:
         """
         Compute count of group, excluding missing values.
 
@@ -3459,7 +3461,7 @@ def shift(self, periods=1, freq=None, axis=0, fill_value=None):
     @final
     @Substitution(name="groupby")
     @Appender(_common_see_also)
-    def diff(self, periods: int = 1, axis: int = 0) -> Series | DataFrame:
+    def diff(self, periods: int = 1, axis: int = 0) -> NDFrameT:
         """
         First discrete difference of element.