How to use GPU as much as possible for faster rendering?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

I am very grateful to this Repo and authors.

Currently I am using the Open3D's new rendering api (gui). And I enable webrtc_server (test in local machine).

I found that its usage of CPU and Memory is higher than the GPU. The screenshot is below.


### **Is there any skill to assign the rendering tasks more to the GPU?**

I have tried to use t.geometry.PointCloud and let the device be 'cuda'. But it out put a warining.

I am trying to visualize a dynamic Point Cloud. Currently I do this by `widget3d.scene.remove_geometry` and `widget3d.scene.add_geometry` at every data update round. I think this way would slow down the rendering as well.

Thank you so much.