Backrooms is an extremely original horror film. It makes last year's much-talked-about Weapons look prosaic in comparison. It's very abstract in a way that a late 20th century horror enthusiast would have a hard time wrapping their head around. A good example of culture getting smarter, not allegedly dumber.
The backrooms as repository for people's blurry, vague memories of others and of place, and an outlet for their worst impulses as embodied in various humanoid creature thingies, is nifty. The best explanation I have for why it's a physical place is that it exists in a different universe, and that these "doorways" (from a furniture store, etc.) are a way of getting there. These doorways are apparently proliferating, but there's no evidence so far that the danger inside the backrooms is escaping into our world. But it's a still a threat in that it can attract, trap and break the minds of people who enter it.
I do wonder just how much the backrooms is totally constituted by generic office building design. Like, can you enter the backrooms from a castle in Germany and see backrooms that looks like an endless iteration of that castle? And if you remain in there long and survive, can you make your way to the kind of backrooms seen in the movie?
Anyway this movie is a nerd's paradise of contemplation.