diff --git a/pypdf/generic/_data_structures.py b/pypdf/generic/_data_structures.py
index 198d15443..a61ac547b 100644
--- a/pypdf/generic/_data_structures.py
+++ b/pypdf/generic/_data_structures.py
@@ -47,7 +47,6 @@
 from .._utils import (
     WHITESPACES,
     StreamType,
-    deprecation_no_replacement,
     logger_warning,
     read_non_whitespace,
     read_until_regex,
@@ -217,12 +216,8 @@ def __isub__(self, lst: Any) -> Self:
         return self
 
     def write_to_stream(
-        self, stream: StreamType, encryption_key: Union[None, str, bytes] = None
+        self, stream: StreamType
     ) -> None:
-        if encryption_key is not None:  # deprecated
-            deprecation_no_replacement(
-                "the encryption_key parameter of write_to_stream", "5.0.0"
-            )
         stream.write(b"[")
         for data in self:
             stream.write(b" ")
@@ -494,17 +489,13 @@ def xmp_metadata(self) -> Optional[XmpInformationProtocol]:
         return XmpInformation(metadata)
 
     def write_to_stream(
-        self, stream: StreamType, encryption_key: Union[None, str, bytes] = None
+        self, stream: StreamType
     ) -> None:
-        if encryption_key is not None:  # deprecated
-            deprecation_no_replacement(
-                "the encryption_key parameter of write_to_stream", "5.0.0"
-            )
         stream.write(b"<<\n")
         for key, value in self.items():
             if len(key) > 2 and key[1] == "%" and key[-1] == "%":
                 continue
-            key.write_to_stream(stream, encryption_key)
+            key.write_to_stream(stream)
             stream.write(b" ")
             value.write_to_stream(stream)
             stream.write(b"\n")
@@ -984,12 +975,8 @@ def hash_value_data(self) -> bytes:
         return data
 
     def write_to_stream(
-        self, stream: StreamType, encryption_key: Union[None, str, bytes] = None
+        self, stream: StreamType
     ) -> None:
-        if encryption_key is not None:  # deprecated
-            deprecation_no_replacement(
-                "the encryption_key parameter of write_to_stream", "5.0.0"
-            )
         self[NameObject(SA.LENGTH)] = NumberObject(len(self._data))
         DictionaryObject.write_to_stream(self, stream)
         del self[SA.LENGTH]
@@ -1663,12 +1650,8 @@ def dest_array(self) -> "ArrayObject":
         )
 
     def write_to_stream(
-        self, stream: StreamType, encryption_key: Union[None, str, bytes] = None
+        self, stream: StreamType
     ) -> None:
-        if encryption_key is not None:  # deprecated
-            deprecation_no_replacement(
-                "the encryption_key parameter of write_to_stream", "5.0.0"
-            )
         stream.write(b"<<\n")
         key = NameObject("/D")
         key.write_to_stream(stream)
diff --git a/pypdf/generic/_outline.py b/pypdf/generic/_outline.py
index d5d4bb132..fb7426b66 100644
--- a/pypdf/generic/_outline.py
+++ b/pypdf/generic/_outline.py
@@ -1,18 +1,12 @@
-from typing import Union
-
-from .._utils import StreamType, deprecation_no_replacement
+from .._utils import StreamType
 from ._base import NameObject
 from ._data_structures import Destination
 
 
 class OutlineItem(Destination):
     def write_to_stream(
-        self, stream: StreamType, encryption_key: Union[None, str, bytes] = None
+        self, stream: StreamType
     ) -> None:
-        if encryption_key is not None:  # deprecated
-            deprecation_no_replacement(
-                "the encryption_key parameter of write_to_stream", "5.0.0"
-            )
         stream.write(b"<<\n")
         for key in [
             NameObject(x)