# UNDF: UNDF-2026-000001206
--- a/cura/Settings/SettingInheritanceManager.py
+++ b/cura/Settings/SettingInheritanceManager.py
@@ -1,6 +1,6 @@
 # Copyright (c) 2017 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
-from typing import List, Optional, Set, TYPE_CHECKING
+from typing import List, Optional, Set, TYPE_CHECKING, cast

 from PyQt6.QtCore import QObject, QTimer, pyqtProperty, pyqtSignal
 from UM.FlameProfiler import pyqtSlot
@@ -29,7 +29,9 @@ class SettingInheritanceManager(QObject):
     def __init__(self, parent = None) -> None:
         super().__init__(parent)

         self._global_container_stack = None  # type: Optional[ContainerStack]
-        self._settings_with_inheritance_warning = []  # type: List[str]
+        # Use a set for O(1) membership checks — fired on every property change.
+        self._settings_with_inheritance_warning = set()  # type: Set[str]
         self._active_container_stack = None  # type: Optional[ExtruderStack]

         self._update_timer = QTimer()
@@ -57,7 +59,7 @@ class SettingInheritanceManager(QObject):
         result = []
         for key in definitions[0].getAllKeys():
             if key in self._settings_with_inheritance_warning:
                 result.append(key)
         return result

     @pyqtSlot(str, str, result = bool)
@@ -87,19 +89,19 @@ class SettingInheritanceManager(QObject):

     @pyqtSlot(str)
     def manualRemoveOverride(self, key: str) -> None:
-        if key in self._settings_with_inheritance_warning:
-            self._settings_with_inheritance_warning.remove(key)
+        if key in self._settings_with_inheritance_warning:  # O(1) set lookup
+            self._settings_with_inheritance_warning.discard(key)
             self.settingsWithIntheritanceChanged.emit()

     @pyqtProperty("QVariantList", notify = settingsWithIntheritanceChanged)
     def settingsWithInheritanceWarning(self) -> List[str]:
-        return self._settings_with_inheritance_warning
+        return list(self._settings_with_inheritance_warning)

     def _onPropertyChanged(self, key: str, property_name: str) -> None:
         if (property_name == "value" or property_name == "enabled") and self._global_container_stack:
             definitions = self._global_container_stack.definition.findDefinitions(key = key)  # type: List["SettingDefinition"]
             if not definitions:
                 return

             has_overwritten_inheritance = self._settingIsOverwritingInheritance(key)

             settings_with_inheritance_warning_changed = False

             # Check if the setting needs to be in the list.
-            if key not in self._settings_with_inheritance_warning and has_overwritten_inheritance:
-                self._settings_with_inheritance_warning.append(key)
+            if has_overwritten_inheritance:
+                added = key not in self._settings_with_inheritance_warning
+                self._settings_with_inheritance_warning.add(key)  # O(1) no-op if present
                 settings_with_inheritance_warning_changed = True
-            elif key in self._settings_with_inheritance_warning and not has_overwritten_inheritance:
-                self._settings_with_inheritance_warning.remove(key)
+            elif not has_overwritten_inheritance and key in self._settings_with_inheritance_warning:
+                self._settings_with_inheritance_warning.discard(key)  # O(1) remove
                 settings_with_inheritance_warning_changed = True

             parent = definitions[0].parent
@@ -110,12 +112,12 @@ class SettingInheritanceManager(QObject):
             else:
                 parent = definitions[0]  # Already at a category

-            if parent.key not in self._settings_with_inheritance_warning and has_overwritten_inheritance:
+            if has_overwritten_inheritance and parent.key not in self._settings_with_inheritance_warning:
                 # Category was not in the list yet, so needs to be added now.
-                self._settings_with_inheritance_warning.append(parent.key)
+                self._settings_with_inheritance_warning.add(parent.key)  # O(1)
                 settings_with_inheritance_warning_changed = True

-            elif parent.key in self._settings_with_inheritance_warning and not has_overwritten_inheritance:
+            elif not has_overwritten_inheritance and parent.key in self._settings_with_inheritance_warning:
                 # Category was in the list and one of it's settings is not overwritten.
                 if not self._recursiveCheck(parent):  # Check if any of it's children have overwritten inheritance.
-                    self._settings_with_inheritance_warning.remove(parent.key)
+                    self._settings_with_inheritance_warning.discard(parent.key)  # O(1)
                     settings_with_inheritance_warning_changed = True

             # Emit the signal if there was any change to the list.
@@ -140,7 +142,7 @@ class SettingInheritanceManager(QObject):

     def _update(self) -> None:
-        self._settings_with_inheritance_warning = []  # Reset previous data.
+        self._settings_with_inheritance_warning = set()  # Reset previous data.

         # Make sure that the GlobalStack is not None. sometimes the globalContainerChanged signal gets here late.
         if self._global_container_stack is None or self._active_container_stack is None:
@@ -151,13 +153,13 @@ class SettingInheritanceManager(QObject):
         all_keys = self._active_container_stack.getAllKeys()
         for setting_key in self._active_container_stack.getAllKeysWithUserState():
             if self._userSettingIsOverwritingInheritance(setting_key, self._active_container_stack, all_keys):
-                self._settings_with_inheritance_warning.append(setting_key)
+                self._settings_with_inheritance_warning.add(setting_key)  # O(1) insert

         # Check all the categories if any of their children have their inheritance overwritten.
         for category in self._global_container_stack.definition.findDefinitions(type = "category"):
             if self._recursiveCheck(category):
-                self._settings_with_inheritance_warning.append(category.key)
+                self._settings_with_inheritance_warning.add(category.key)  # O(1) insert, dedup free

         # Notify others that things have changed.
         self.settingsWithIntheritanceChanged.emit()