Tomas Slancik

you may need to define an upvector

I'm not sure you can do that with shadow linking
to me shadow linking looks like you can decide which objects do or do not cast shadows from a particular light or collection of lights
not necessarily which objects cast shadows onto which other objects

so if you exclude your diffuser from any light it will not cast shadows from that light to any objects, not just to your background

you can also do -shadow in Render Visibility if you don't want it to cast shadows at all from any light

you should see stuff update when within Vellum Solver SOP, and since the dive target is DOP context you can do a lot there

however there were builds where diving inside any solver just stops updating viewport, so its likely you are on one of those builds

in such cases I usually lock the viewport when in SOPs looking on the output of the solver and then dive inside and do some work, while you can't see the guides, it's still better than no update at all