How can I make an object only visibile if you look through some
Franky, probably the easiest way is to use blueprint to hide/unhide the objects.
Also, I don’t know if you’ve seen this asset:
Use a scene capture to a texture and apply it as a material to your class. depending on your need you can add a trigger before the class to toggle the visibility of the cubes, like onEnter make them visible, onExit hide them again. In a SceneCapture you can also select which actors it should make visible in the texture which is quite powerfull