While I generally think Mary's room doesn't prove anything, it's not strictly nonsense as a thought experiment, it only seems like nonsense if you already assume that everything can be described by a physical theory. Then of course vision and feelings and all of our experiences must be physical. The point of Mary's room is to test the plausibility of this assertion.
It seems very implausible to many people that anyone studying physics, biology and anatomy for any length of time in a black and white room would ever truly understand the experience of colour. Or as another example, do you think studying physics for any length of time will yield an understanding of what it's like to ride a thrilling rollercoaster or sky dive? Doesn't it seem somewhat plausible that such descriptions wouldn't be able to capture something about those experiences?
There are a number of possible responses to such challenges. One is to say that experiencing redness is not actually knowledge but an ability, so no amount of factual study will yield competency, only exposure will (like riding a bike).
Another is as you sort of implicitly assert, is that the very question assumes a kind of infinite knowledge, which humans are terrible at reasoning about. Mary would be able to describe what she'd say in response to any question about colour, but she wouldn't actually understand her answers? This is the kind of paradox that hints at a poorly formed question.
There are plenty more, but the point is that there's something interesting being discussed here, and we're not yet sure what it is, so the thought experiment currently only serves to identify what camp you belong to, ie. strict physicalists, or dualists, or epiphenomenalists, etc.
That's literally the point of the thought experiment. Thought experiments are mostly nonsense, the point is to help differentiate different phenomenon through extreme, contrived examples. The point here is that despite knowing the entirety of the corpus of knowledge about colour vision, she still doesn't know everything that there is to know about it if she hasn't actually experienced seeing the colour red.
> The point here is that despite knowing the entirety of the corpus of knowledge about colour vision, she still doesn't know everything that there is to know about it if she hasn't actually experienced seeing the colour red.
But that isn't the point being made in the article. The point being made is that this is somehow non-physical, which is obviously wrong:
Thus, argues Jackson, Mary has come to know a non-physical fact; so proving that not all knowledge is physical.
The premise is that Mary knows everything there is to know about colour vision. If this is true, then she knows what it is like to see colour.
If she doesn't know that, then the premise is false.
It's just nonsense.