Disable daynight themes entirely

app/src/main/res/values-night/themes_daynight.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-<!--
   <style name="Theme.ChatTheme.Material_DayNight" parent="Theme.ChatTheme.Material_Dark" />
   <style name="Theme.ChatTheme.Quassel_DayNight" parent="Theme.ChatTheme.Quassel_Dark" />
   <style name="Theme.ChatTheme.Solarized_DayNight" parent="Theme.ChatTheme.Solarized_Dark" />
   <style name="Theme.ChatTheme.Gruvbox_DayNight" parent="Theme.ChatTheme.Gruvbox_Dark" />
--->
 </resources>

app/src/main/res/values-v28/strings_preferences.xml

@@ -18,6 +18,7 @@
   -->
 
 <resources>
+  <!--
   <string-array name="preference_theme_entries" translatable="false">
     <item>@string/preference_theme_entry_material_daynight</item>
     <item>@string/preference_theme_entry_material_light</item>
@@ -50,4 +51,5 @@
     <item>GRUVBOX_DARK</item>
     <item>DRACULA</item>
   </string-array>
+  -->
 </resources>