No version of Rhino has ever been officially supported when used with any virtual machine.
Various users have attempted to run Rhino virtualized anyway and discovered that in many (most) cases with Rhino versions up to Rhino 5 it worked well enough for them.
With Rhino 6 there is too large a disparity between Rhino’s required OpenGL capabilities and that provided by the latest version of Parallels on Macs to provide a useful user experience - as you have discovered. It is not known when Parallels will catch up, or indeed if ever. Apparently Apple has announced they are not going to provide any further updates to OpenGL, which will seriously complicate Parallel’s ability to provide reasonably up-to-date OpenGL features. My understanding is that Parallels is at present trying to decide whether up-to-date OpenGL is important to enough of their users and potential users to warrant the development effort.
If it’s important to you I suggest a note to Parallels support with your thoughts.
I doubt that McNeel will take much interest in our plight as they have put an enormous amount of effort into a Mac version of Rhino and V6 is the first one that is intended to provide the same capability as the Windows version. They’d probably rather sell you that.