SUMMARY Currently, when using pulseaudio and configuring sound settings, it is possible to create virtual devices. However, the UI is absent if the backend used is pipewire. With pipewire now supporting native module-combine-stream (https://gitlab.freedesktop.org/pipewire/pipewire/-/tags/0.3.65), the feature should be made accessible via GUI for feature parity.
With pipewire is also absent a more basic switch to deviate the output on last inserted device.
Besides module-combine-stream, pipewire is still missing module-gsettings so that we can change these settings (at least in a compatible way with the current pulseaudio interface). The integration of this module seems to be in progress though (https://gitlab.freedesktop.org/pipewire/pipewire/-/merge_requests/1468)
Related https://bugs.kde.org/show_bug.cgi?id=440536
> pipewire is still missing module-gsettings so that we can change these settings it has been added a year ago afaik: https://docs.pipewire.org/page_pulse_module_gsettings.html