^ I guess that the Rhino developers could give the most complete answer. Raytracing engines such like Keyshot use a denoiser for the real-time rendering.
Rendered mode and most display modes are not with raytracing engines. The only standard display mode we provide with that capability is called… Raytraced.
Denoisers do not work on non-raytraced display modes. In Raytraced mode you’ll see in the HUD a small star. When that is on the denoiser can be applied assuming it is enabled, which it typically is. Rhino comes with the intel denoiser, since it is CPU based.
The denoiser works with the real-time raytracing mode. It must be enabled manually from the Properties panel. It was off by default. However, I see zero difference with and without it. The denoising works with the same speed in either way.
In the case you mean Raytraced then indeed yes. Rendered, no.
It really depends on what you are trying to render in Raytraced or Rhino Render to be able to see that. Also the sample amount should be taken into consideration. It is to get less grainy results, so with grainy input you’ll see better results, typically.