Mine shows up as an available device (despite the fact I only use it as SPDIF... so it has to be unselected to use my 18i6 instead).
Two thoughts (edit: 3+ eleventy thoughts... lulz)....
1) Do you have another Focusrite interface installed? If so this can be confusing in the Prefs menu. You'll see both devices listed but the names are very similar. It's tripped me up when switching from Voicemeeter to the 18i6 before. However if you are in ASIO you can only choose on at a time so it quickly becomes apparent quite quickly (one will block the other from being selected in Prefs).
2) Did you install correctly? Look at the VRM box install instructions to see if you missed any of the install Voodoo needed to make it work as an interface. If unsure uninstall and reinstall following the directions to the LETTER.
3) Maybe you need to run the Sonar Audio Device/Wave Profiler thingie? Maybe you need to enable the device in the Windows Control Panel > Sounds section (or whatever it is in 10 if you use that)? Maybe you need to reboot and connect the VRM Box BEFORE opeing Sonar (as opposed to connecting it AFTER opening Sonar or opening Sonar too quickly after connecting the VRM)? Maybe you are switching USB ports and making the system/Sonar play hide and seek with the ports?
Okay I guess that last one was a bunch of thoughts but just some general troubleshooting I'd try.
Cheers.