Why would one want to do this? What is the point of an audio-endpoint isolated inside a virtual machine without connection to the outside world? How do you want to listen to your music playing?
Because the virtual graphics card lacks support for the needed OpenGL? You may have to give the VM access to a physical GPU to overcome that issue. You may also have to give the VM access to a physical interface (USB-port or sound-card) to play music (to use Roon inside the VM as endpoint by your initial request).
You know, other Linux and Roon users use Wine (as suggested by Roon Labs):
For some the (virtual) audio devices seen by Roon inside Wine even work out-of-the-box for playback on the local PC, for others they don’t. So far no user has presented a recipe to make them work for all installations. In this case there is still the Roon Bridge for Linux available for download and install should you need local playback functionality.
Note: For some users the (technically outdated) Linux Roon Bridge lead to system lock-ups though on newer distributions.
PS: Roon Labs may suggest the use of Wine for Linux users but that sadly doesn’t make it supported though.