I would take a look at the LS10 manual before going much further though. This could be a setting issue.
Also, this may be an issue of making sure the LS10 is on before you turn on your Roon Nucleus.
There is some handshaking involved in USB (as well as HDMI) audio. If my DAC is off before I turn on my streamer it won’t ever be seen. In my case it has to do with the Linux OS does a device scan on startup only. Any audio devices attached after that process is completed won't make it to the device registry.