I really like what you've done with the Backrooms concept! It makes the backrooms a lot less horror-like. It reminds me of 'in-between world' that Lewis describes.

I've always loved the idea of it, and I've slowly created my own head canon, I've just been waiting for a good time to put it on paper, haha. I also really like the idea that the backrooms are connected to the SCP foundation through "The Infinite Ikea."

Basically, the reason that SCPs exist in our world is that they slipped through the backrooms in their world, and slipped through to ours. That explains why similar SCPs are so rare, but overall they are common.

The chances of multiple creatures slipping from one realm is extremely rare, but when you have infinite realms, the chances are alot higher that at least one has fallen through from one of a million worlds, and when you have infinite worlds, it makes sense why there are so many from so many different universes.

To me the backrooms isn't scary as much as it is dreadful. You will find the monsters, yes, but the real terror comes from the concept of it all.