If you’re able to select rytm as both your recording device and your playback device and you can successfully monitor all channels so that you’re hearing the master track (which is what you want to record) then try changing your host from MME to windows wasapi and then select rytm for loopback recording, then set your stereo track and arm record, when you play it should begin recording via the loopback.
This is how you record audio sources inside your computer that don’t have a direct input to audacity, as an example youtube audio. It’s recording directly from the soundcard so I assume it will work the same with rytm as the interface. I’m pretty sure it should give you an option that says something like Line in (elektron analog rytm) (loopback) and that’s what you want to select.
I assume you’re doing whatever correctly, but I don’t know how to tell you to set up rytm to record the master track - with digitone and other digi boxes you can just select the device and arm the track then record and it defaults to the master out.
If you’re unable to figure out why rytm is only recording bd and sd, and the other criteria are met then you can try this as a workaround.