I think it would be very useful to have a plain, featureless door with Canvas Functionality. It’d essentially just be a Canvas that rotates like a door without a frame.
Preferably it wouldn’t have the “Open” prompt when hovering over it and would have the ability to enable a picture frame (similar to the default Canvas) so players could hide passages behind paintings.
Here’s just some simple mockups to better explain the idea.
(As a door)
(As a Painting)