point user to manual if they're trying to disable night mode in dark mode

qt/aqt/preferences.py

@@ -10,6 +10,7 @@ import aqt
 from anki.lang import _
 from aqt import AnkiQt
 from aqt.qt import *
+from aqt.theme import theme_manager
 from aqt.utils import TR, askUser, openHelp, showInfo, showWarning, tr
 
 
@@ -234,6 +235,11 @@ Not currently enabled; click the sync button in the main window to enable."""
         self.form.pasteInvert.setChecked(self.prof.get("pasteInvert", False))
         self.form.showPlayButtons.setChecked(self.prof.get("showPlayButtons", True))
         self.form.nightMode.setChecked(self.mw.pm.night_mode())
+        if theme_manager.macos_dark_mode():
+            self.form.nightMode.setChecked(True)
+            self.form.nightMode.setText(tr(TR.PREFERENCES_DARK_MODE_ACTIVE))
+        else:
+            self.form.nightMode.setChecked(self.mw.pm.night_mode())
         self.form.interrupt_audio.setChecked(self.mw.pm.interrupt_audio())
 
     def updateOptions(self):
@@ -247,9 +253,17 @@ Not currently enabled; click the sync button in the main window to enable."""
             restart_required = True
         self.prof["showPlayButtons"] = self.form.showPlayButtons.isChecked()
 
-        if self.mw.pm.night_mode() != self.form.nightMode.isChecked():
-            self.mw.pm.set_night_mode(not self.mw.pm.night_mode())
-            restart_required = True
+        if theme_manager.macos_dark_mode():
+            if not self.form.nightMode.isChecked():
+                # user is trying to turn it off, but it's forced
+                showInfo(
+                    tr(TR.PREFERENCES_DARK_MODE_DISABLE), textFormat="rich",
+                )
+                openHelp("profileprefs")
+        else:
+            if self.mw.pm.night_mode() != self.form.nightMode.isChecked():
+                self.mw.pm.set_night_mode(not self.mw.pm.night_mode())
+                restart_required = True
 
         self.mw.pm.set_interrupt_audio(self.form.interrupt_audio.isChecked())
 

qt/ftl/preferences.ftl

@@ -0,0 +1,7 @@
+# shown instead of the 'night mode' option when night mode is forced on because
+# macOS is in dark mode
+preferences-dark-mode-active = macOS is in dark mode
+
+preferences-dark-mode-disable =
+  To show Anki in light mode while macOS is in dark mode, please
+  see the Night Mode section of the manual.