In other words, "You can't derive 1st-person qualia from 3rd-person physics alone."
I've studied this for decades and it's a recurring theme not only with Jackson's "Mary" thought experiment, but with Nagel's "Bat", Searle's "Chinese Room", Leibniz's "Mill", etc.
The reason these arguments are often difficult to appreciate is because we struggle to put ourselves in the minds of other people, wondering how/if they perceive the world, but all the while we are using terms whose meanings and experiences we already understand intimately (e.g. red, rose, tomato... in the case of the Mary argument.)
The argument would have a bit more force if you imagined yourself landing on a strange new planet inhabited by Zorlichs. Zorlichs often drink Byzerp, which is a beverage made from Slayrne, Mucche, and Karlne. You're an expert molecular chemist. You've studied these ingredients for months and you now know all there is to know about Slayrne, Mucche, and Karlne. You know how they interact not only with each other but also with human biology (e.g. you'll know at least whether this beverage would harm you or not). Oh, you also happen to be a very picky person. Your entire life, you've never consumed any food or beverage that wasn't entirely bland. That means, you yourself have never had anything sweet, salty, bitter, or fizzy. So the question is: Would you know/learn something new to YOU upon first tasting Byzerp?
If we take "learn" to mean "acquire new experiences", then Mary certainly learns something new upon seeing red for the first time. Keep in mind that people can (and often do) learn something that is fleeting in time: you might have "taught" me how to bake brownies last year and, in that moment, I truly understood... that is too say, I was following along and comprehended every step along the way. But now it's 2023 and I've done nothing with that experience since. Indeed, I kinda forgot most of it. Is it now fair to say of me that I "know" how to make brownies?
"I learned" doesn't necessarily mean "I know".
And that flows both ways. Mary "knows" all there is to know about colour vision because she studied 3rd person objective facts about the world: light waves, retinas, brains, etc. But, if we stick with my definition of "learn" (i.e. "acquire new experiences") then Mary obviously hasn't learned what it is like to have a 1st-person red rose experience until she has that very experience.
That's not to say all learning must be a direct 1st person experience of the matter. I can learn all about the objective facts of skydiving without having experienced it firsthand. But I'll never know the subjective qualia of falling out of a plane towards the earth below until I actually do it.
Mary would have thought: "I don't know what it's like to see red." in the same way I currently think "I don't know what it's like to skydive". Yet both or worlds would be rocked (that is too say "learn something new") upon actually having the experience.