aliases: fix oxygen-icons5 alias (#390189)

pkgs/top-level/aliases.nix

@@ -55,7 +55,7 @@ let
       konversation korganizer kpkpass krdc kreversi krfb kscreen kscreenlocker
       kshisen ksquares ksshaskpass ksystemlog kteatime ktimer ktorrent ktouch
       kturtle kwallet-pam kwalletmanager kwave kwayland-integration kwin kwrited
-      marble merkuro milou minuet okular oxygen oxygen-icons5 picmi
+      marble merkuro milou minuet okular oxygen picmi
       plasma-browser-integration plasma-desktop plasma-integration plasma-nano
       plasma-nm plasma-pa plasma-mobile plasma-systemmonitor plasma-thunderbolt
       plasma-vault plasma-workspace plasma-workspace-wallpapers
@@ -1156,6 +1156,14 @@ mapAliases {
   OSCAR = oscar; # Added 2024-06-12
   osxfuse = throw "'osxfuse' has been renamed to/replaced by 'macfuse-stubs'"; # Converted to throw 2024-10-17
   ovn-lts = throw "ovn-lts has been removed. Please use the latest version available under ovn"; # Added 2024-08-24
+  oxygen-icons5 = throw ''
+    The top-level oxygen-icons5 alias has been removed.
+
+    Please explicitly use kdePackages.oxygen-icons for the latest Qt 6-based version,
+    or libsForQt5.oxygen-icons5 for the deprecated Qt 5 version.
+
+    Note that Qt 5 versions of most KDE software will be removed in NixOS 25.11.
+  ''; # Added 2025-03-15;
   oysttyer = throw "oysttyer has been removed; it is no longer maintained because of Twitter disabling free API access"; # Added 2024-09-23
 
   ### P ###