The ray cast algorithm is expensive to perform at higher resolutions with complex scenes. I would recommend the following options to optimize:

• If you have frame range querying enabled, increase the frame step (do not worry if your active camera changes, those frames are always added, even if they are not on the frame interval)
  
• Reduce the number of bounces
  
• Increase the tile size
• Reduce the number of objects selected. Also, instances, meshes, metaballs, and font object types are much faster to evaluate compared to other object types, so removing other object types from your selection will improve performance.

This is likely a case where the resolution scale is too low. Try increasing the scale in small increments.

The undo functionality works for all nView operators. But if you went beyond your undo size or do not want to undo other operations, the clean panel will allow you to show all objects and collections, as well as remove visibility attribute keyframes.

No, it does not. If you want to hide objects in real-time, check out my free nView Live add-on!

This addon is independent of the render engine. It casts rays internally and applies changes at the scene level. So you can use whatever render engine you want!