Just trying out rhino6, been using 5 for years and objects are now vanishing from all viewports on both screens. I can still select them if I click where they should be and the properties shows them as they should be, just not visible. They seem to reappear for a time when exploded and joined, then vanish again. They seem to be objects created from a recent command, copy and paste from an inserted drawing, a boolean, create uv curves polylines etc. It doesnt look like your described video hardware and driver problems but here is what i’ve been using.
I checked and Windows thinks it already has the best driver installed. Also it just doesnt look like a video or display problem. It is more like rhino is choosing not to show the objects. And I’m quite familiar with hidden objects and clipping planes. They just vanish in front of your eyes but if selected the properties show in the properties panel. Exploding makes them visible again, usually.
Same problem here (Rhino 7, Mac, no mods) and couldn’t find a solution other than retrieving a previous save (which opens another Pandora box of problems).
I noticed that most of the time, it’s all the objects on a layer that disappear, are un-selectable.
Mac Guyver fix: select objects in layer by right-clicking the layer (gumball appears), copy them to a new layer (they magically reappear), put same colour, copy the name of layer 1, delete it, paste name in layer 2.
Hope this helps!
MacOS Mojave, recent powerful iMac, Rhino Version 7 (7.0.20314.03002)