How to get DisplayPort-Audio Working?

I bought a USB-C monitor with a audio-line-out jack. When I connect the monitor to my MacBook Pro, the audio-output get’s recognized immediately as a DisplayPort-output. However, when I connect my ThinkPad to the monitor running NixOS with pipewire, I don’t see an audio-output for the monitor in KDEs menus.

I’ve configured pipewire like so:

security.rtkit.enable = true;

services.pipewire = {
  enable = true;
  alsa.enable = true;
  pulse.enable = true;

Should pipewire not be ready to be used with DP-audio, I would also switch back to pulseaudio if necessary.