I remember that while using Rhino 5, when I selected any component in GH, the preview of said component would always be on top of Rhino geometry.
Now in Rhino 6 something changed and that is no longer the case.
No matter the Display Mode, if it is wireframe, shaded, etc. GH geometry is always behind, and I cannot see it unless I hide or delete Rhino objects…
… Sorry, I can’t tell.
If I had that problem, I would have probably uninstall (clean) and reinstall both, gpu drivers and rhino…
I hope you’ll receive some help from the developers.