You can use the service hatch if you insert it using the arrow keys on the keyboard.
You could also use an invisible box that you import as a door/window.

Hello,

Thanks so much for the quick reply! I have tried both methods you have mentioned, but unfortunately, they didn't make any difference to what I had attempted previously.

Adding the service hatch with either the mouse or arrow keys provides the same results - a hole through the entire wall.

And as I had mentioned in my original post, if I import the "invisible box" as a door/window, it also is very much "visible" as a complete hole through both sides of the wall. If it was only visible on one side, it would be perfect, but regretfully this is not the case.