“I imagine pointing the camera at the ceiling and then walking through the door, paying attention that the remaining part of the wall above the lintel does not obscure too much or throws shadows.”
Unfortunately, if using flash, while still in Room A, I’ve found that’s exactly what does throw deep shadow onto the nearest visible bits of Room B - and as you pass under the door head into Room B, the shadow switches onto nearest visible bits of Room A. So the same features look maybe unrecognisably different.
With a single flash unit, that’s true whether the flash is on or off camera - just depends which room it’s in. Unfortunately I don’t at present have off-camera flash facility. Maybe with two flash units one in ea room. Or single off-camera flash unit exactly on the door threshold looking up, if the wall has little thickness.
Still, will try again.
If, in the first idea, relying on far wall seen through the doorway, need to well iluminate both rooms at same time? Two flash units again.