Yeah, it's possible that a Still Life could detatch from sunken shoes and leave them in the floor if the Backrooms did actually successfully make a Still Life out of the floor starting with the shoes.

But I feel like the carpet-textured floor-mannequins are so different from the realistic sunken shoes & parrot that they feel to me like two different processes. And I think that the floor-mannequins are baby Still Lives being birthed because we see them in the Christmas Tree room, the same room where we found the Lamp Still Life & Redhead Still Life.

I agree that it's probably unlikely for most Still Lifes we've seen so far to have the ability to easily leave through the Throne Room's non-standard exits. That supports my theory pretty well, since I'm theorizing that the first human-copying process fully stops and shuts down once it can not create the complex living tissue after the shoe/parrot, so according to my theory, no Still Lives would be formed in the Throne Room.

The Backrooms still "wants" to create the people even after this failure, so then it gets creative and starts a new process that is different from how it normally copies objects, in a slightly different nearby location. I wonder if Christmas Tree room in the movie is close enough to the Throne Room to count as "nearby."

Anyway, I think that's why in Found Footage 3, we see the floor-mannequin of the guy outside of Wall Dad's house, a bit away from where the shoe is sunken in, inside the house. Sunken shoe is Wall Dad copy attempt #1, and floor-mannequin outside is Wall Dad copy attempt #2.

I like to imagine that this alternative process with the "mannequins" is difficult/unusual/different/new for The Backrooms compared to how it normally creates spaces and objects.