Describe the bug
When running VirtualBox I get the error "Qt FATAL: Cannot mix incompatible Qt library (version 0x50c07) with this library (version 0x50e02)", which means that there are two incompatible library versions of Qt involved: 5.12 (0x50c) and 5.14 (0x50e).
I'm using the plasma desktop on 20.09beta.

To Reproduce
Steps to reproduce the behavior:

1. services.xserver.desktopManager.plasma5.enable = true;
   virtualisation.virtualbox.host.enable = true;
2. Try to start VirtualBox from a terminal in Plasma.

Expected behavior
VirtualBox shows its graphical interface.

Screenshots

$ LANG=C VirtualBox
Qt FATAL: Cannot mix incompatible Qt library (version 0x50c07) with this library (version 0x50e02)
Aborted (Speicherabzug geschrieben)

Notify maintainers

Metadata

• system: "x86_64-linux"
• host os: Linux 5.4.70, NixOS, 20.09beta1181.a8da27d4b07 (Nightingale)
• multi-user?: yes
• sandbox: no
• version: nix-env (Nix) 2.3.7
• channels(root): "nixos-20.09beta1181.a8da27d4b07"
• channels(user): ""
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

$ (sudo nix-env -q; nix-env -q) | wc -l
0

Maintainer information:

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