All the tutorial I found were on unity but I’m trying to replicate it in Unreal.
I can already spawn a room in AR but have no clue on how to mask it when viewed from outside.
The unity tutorial use the stencil buffer as a solution. Is there something equivalent in Unreal?
Unreal has custom z-buffers that lets you generate masks for objects for the purposes of adding things like outlines, I think you probably can use it to create a mask that will replace the masked parts with a feed from the camera in a post-process material. Another possibility is to use the render target functionality to add the material displaying it to the mesh directly. I do not know if it is possible to pull external video feed inside the unreal, though.