Describe the bug
Since 20.09, when i try to use KGPG (nix-shell -p kgpg), KMail (nix-shell -p kmail) or Kontact (nix-shell -p kontact)

I get

error: Package ‘breeze-qt5-5.18.5’ in /nix/store/fvik248l0i6x4y1kln813fqhh7cdj4cq-nixos-20.09.1500.edb26126d98/nixos/pkgs/desktops/plasma-5/default.nix:96 is marked as broken, refusing to evaluate.

a) For `nixos-rebuild` you can set
  { nixpkgs.config.allowBroken = true; }
in configuration.nix to override this.

b) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowBroken = true; }
to ~/.config/nixpkgs/config.nix.

(use '--show-trace' to show detailed location information)

To Reproduce
Steps to reproduce the behavior:

1. nix-shell -p kgpg

Expected behavior
Applications should work

Additional context
I don't know if i should report in new issue (like this) or in this issue #102340

Notify maintainers

Metadata

• system: "x86_64-linux"
• host os: Linux 5.4.72, NixOS, 20.09.1500.edb26126d98 (Nightingale)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.7
• channels(pinage404): "home-manager-20.09, nixos-20.09.1500.edb26126d98, nixos-unstable-21.03pre249162.1dc37370c48"
• channels(root): "nixos-20.09.1500.edb26126d98"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module: