got rid of that one deprecation warning although there's still the one about optionsDocBook which I don't use in my config

hosts/niks/configuration.nix

@@ -72,7 +72,7 @@ in
     # https://github.com/NixOS/nixpkgs/issues/158025
     security.pam.services.swaylock = {};
 
-    fonts.fonts = with pkgs; [
+    fonts.packages = with pkgs; [
         material-design-icons
         (nerdfonts.override { fonts = [ "JetBrainsMono" ]; })
     ];