The air quotes around tortured are doing 100% of the work here. There may indeed be some nervousness associated with taking part in any sort of competition, but I think most people would stipulate that white collar adult professionals answering 15 multiple-choice questions in 30 minutes in a comfortable studio wearing clothes of their choice, preparing in a green room, given access to water and bathrooms is pretty low on the torture scale. Likewise, we don't typically consider, say, taking part in a poker tournament to be torture, or taking part in a 10K race or submitting something to an art contest.
There are, in fact, quiz shows that add torture elements. Rob Lowe hosts Mental Samurai, which is a quiz show where participants are put through physical disorientation[0]. This might be a closer parallel to what you are highlighting, but even still there are coherent and easily articulated ways in which this is not torture.
There are a great many reality programs that do actually involve a sort of physical depravation which is closer to torture. Big Brother and Survivor both involve not just physical challenges, but also punishments that are centered around depriving people of the sorts of creature comforts they are accustomed to in normal life. Even then you don't have torture, because again the vast majority of the experience involves being treated with comfort and dignity, the punishments that are small in scale and support systems in place to ensure they do not present real threat. So, for instance, you might have someone being awoken in the middle of the night as a part of a challenge, but they will be informed of that in advance, given additional time to sleep later, and the disruption will be minimal.
Mr. Beast's stuff has more in common with challenges like the Hands on a Hardbody challenge[1], where poor people go to a car dealership and have to touch a truck for an extended period of time to win the truck.[1] The contestant pool are mostly people who are quite poor, some of whom seem to be mentally ill, the willingness to do it for the prize almost surely implies they have inadequate access to transportation, and it's extremely undignified. But even this has hourly breaks.
It seems like a bit of feigned ignorance to respond to someone criticizing the Mr. Beast stuff by suggesting it is difficult or impossible to draw a coherent line in the sand, and then offering such a patently absurd example as something you think would have to be definitionally included. It comes off as playing language games rather than seriously engaging the substance of the criticism.
[0] https://www.youtube.com/watch?v=O3gglCEsvGg
[1] https://en.wikipedia.org/wiki/Hands_on_a_Hardbody:_The_Docum...