In death camps, particularly in Auschwitz there was a phrase in camp slang “mussellman” which is the Yiddish word for Muslim. This likely came from how these people would fall on the ground when they could no longer walk in a similar way to the prostration in Muslim prayer. This is discussed in many texts such as Night, Man’s Search for Meaning, and many of Primo Levi’s works. The phrase was meant to describe a person near death, and part of that description includes what you describe. The “mussellmen” didn’t care any more whether they ate, whether they were beaten, whether they were tortured, the process of dying had taken hold and they did not have the energy, will, or mental capacity to survive any longer. On a kind of opposite note there were also people like Filip Mueller who survived years of the psychological torture of being a sonderkommando (a Jewish prisoner forced to help the Nazis get Jews into the gas chambers, then to burn the bodies after) and he discussed in his memoirs a kind of dichotomy where he was not desensitized to the trauma per say, but had come to an in between space where he could survive the torture one day at a time. Children also proved incredibly resilient, Eva Mozes Kor survived medical torture at the hands of Josef Mengele but was able to survive the torture because she knew if she died her twin sister would also be killed. Almost all survivors describe some level of “getting used to” certain kinds of torture such as starvation, cold, and psychological torture. They were not immune to it, they still felt those things and the physical sensations were often overwhelming, but their will to survive was stronger and allowed them to push through extreme pain or starvation. This is one of the many things discussed in Man’s Search for Meaning. Tadusz Borowski’s writings are also really interesting sources on this kind of psychological numbing.

Hope that answered your question, feel free to follow up.