With it being referred to as a physics problem, I thought they were foreshadowing ChatGPT responding that the amount of work done being zero.

I don't know how ChatGPT works, but it often feels like it is making inferences from data and those inferences are reasonable sounding but ultimately incorrect. In this case, it would be conflating work with workout. In one of my experiments, I was asking it about something in a children's book. ChatGPT ended up mixing up something that happened early in the story with something that happened at the end of the story, even though they were unrelated.

If you're not observing the outside world, then the reference frames "at rest" and "moving at a constant speed" are indistinguishable.

Climbing a staircase requires the same amount of work as climbing a down-escalator. The escalator "wants" to accelerate when you do work on it, but instead this work gets dumped into the braking mechanism, in order to maintain a constant speed.

That is a good one. To offer another explanation, one that doesn't involve changing reference frames, note that the step moves down as your foot pushes down on it, which by definition means work is being done.