My take on the ending. Is this a popular take? [SPOILERS]

!Clark asks Mary if she has ever "5150'd" someone, meaning whether she has ever had a patient placed on an involuntary psychiatric hold. Mary says yes, but only in extreme cases. My take is that this foreshadows Clark himself.!<

!I think Mary eventually has to place Clark on a psychiatric hold, and the people doing the MRI scan, or perhaps running the facility, are Async. Maybe Async are testing a treatment, or maybe they have discovered a way to get inside a patient's head, see what they see, visualise it, and interact with their internal reality to understand how it works.!<

!Phil, the Async researcher, reacts when he sees Clark on the TV because he recognises him as a patient. He seems obsessed with Clark, probably because Async are exploring his twisted mind and trying to understand it. There is also the possibility that Phil is excited because this is new technology, or a new procedure, and Clark is the clearest example of it working. Towards the end, Phil sounds almost enthusiastic while talking to Mary. He does not act like someone simply discussing a patient. He acts like someone who knows he has discovered something massive and is trying to explain it without fully revealing how far Async has gone.!<

!I would need to watch the movie again, but it seems possible that Phil is talking to the real Mary at that point and asking her questions about Clark, including anything Clark discussed with her. So that scene could involve the real Mary, while the Mary seen inside the Backrooms is Clark's memory of her.!<

!So I don't think the Backrooms are necessarily a physical place. They may be Clark's psychotic mind made visible. That is why they look the way they do: endless corridors, ugly lighting, pointless rooms, bad proportions, and architecture that feels designed but completely wrong. Clark is a failed architect, so his broken mind creates broken architecture. The fact that the detail of him being a “failed architect” is repeated so many times feels like a clear indicator.!<

!I also don't think Mary is really inside the Backrooms. She is Clark's memory of Mary, which is why she starts to fade and distort towards the end. The same applies to the monster. Clark sees himself as a monster: failed, pathetic, angry, drunk, trapped in a furniture store, trying to make adverts so people buy more meaningless stuff. That’s why the monster looks like that.!<

!The drugs or medical procedure could also explain why everything feels unstable and distorted. The main idea is that Async's MRI procedure lets them explore Clark's mind from the inside. The real Mary may be outside, speaking with Phil. The Mary inside the Backrooms is Clark's memory. The monster is his self-image. The Backrooms are the failed, collapsing mind of a lonely architect who has lost himself!<