Describe the bug
A lot of kde widgets and functions broke after recent updates on the unstable channel (nixos-unstable). Opening the bluetooth widget shows this error message:

Error loading QML file: file:///nix/store/74xnbqp5gmaq5s3b1xs6d7iaahkjrh72-bluedevil-5.17.5/share/plasma/plasmoids/org.kde.plasma.bluetooth/contents/ui/BluetoothApplet.qml:24:1: module "org.kde.bluezqt" is not installed

Other broken widgets/functions includes bluetooth widget, printer widget and desktop (the desktop disappeared resulting in a black background)

xsession log: https://fars.ee/Z2vb

To Reproduce
Steps to reproduce the behavior:

1. Install plasma
2. open plasma

Expected behavior
Plasma widgets should work normally

Screenshots
A broken widget:

Additional context
Add any other context about the problem here.

Notify maintainers

Metadata
Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

• system: "x86_64-linux"
• host os: Linux 5.7.15, NixOS, 20.09pre238896.16fc531784a (Nightingale)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.4pre20200721_ff314f1
• channels(root): "nixos-20.09pre238896.16fc531784a, home-manager"
• 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: services.xserver.desktopManager.plasma5