Invisible wall setup
The course would have been better if the technique of doing the invisible wall room was shown in the video rather than glimpse over it and then provide a file to figure this out. (given this is tagged as a beginner course)
Even within the provided file, the following steps do not work for a new room made with a cube.
1. A cube with Faces flipped
2. Separate the faces closer to the camera - renamed "Invisible Walls"
3. Ray visibility of "Invisible Walls" turned off.
4. The cubical room does not render, but your room does.
Whats the magic here ?