I used to think, "wow this is too good to be true, and so many people do it, can't wait to try!"
Well, all of the doors in my apartment are made of cheap hollow core (a very structurally unsound honeycomb material is used and then cheap thin plywood is applied on top of that); such doors are very flimsy, they can't even be 'slammed' shut because they have so little heft to them. They are very common in what are called 'mid-century' architecture apartment buildings, where mid-century is a stupid marketing term for the 1960s. It's basically a cost-saving measure when building.
I was able to do practice runs off, kneeling away from a doorknob, to see if suspension as a method might be something I can tolerate, but no way would hollow core support me at 170 lbs/77kg for successful cbt. Maybe a very light person?
I would imagine celebrities and such have solid core or solid wood doors in their homes, and if I remember correctly, most hotels do as well.
All about door types:
https://www.thespruce.com/hollow-core-vs-solid-wood-doors-1821449