Comment by pzmarzly

I'm not aware of any plugins, but in case anyone is curious about how to replicate that setup on Linux systems with PulseAudio, you can create virtual outputs with:

    pactl load-module module-null-sink \
        sink_name=Device_Name \
        sink_properties=device.description=Device_Name

If some program filters out output monitors from its input list, you can usually use pavucontrol to force-change it. Or, you can create a linked virtual source:

    pactl load-module \
        module-virtual-source \
        source_name=VirtualMic \
        master=Device_Name.monitor \
        source_properties=device.description=VirtualMic

Then in OBS settings you can set up the virtual device as Monitoring Device.

I took the commands from one of my side projects, maybe someone will find other parts of it interesting: https://github.com/pzmarzly/mic_over_mumble