Occluding rendering with an invisible wall.

Is there an easy way in Unity to have an invisible wall that blocks rendering? I’m trying to create something like this;

Basically it's a portal that you can look through with nothing rendered outside it (making it great for AR applications such as above)

The only other way I can think of for this to work would be to have a rendertexture that renders the output of a camera - but I have a feeling that would look wonky, and wouldn’t make it easy to animate things coming out of it. Ideally I’d like that to be the actual 3d space but just having other objects blocking the rendering somehow.

maybe you can do something with this youtube video, and that the plane followed the player