I'm not sure that we're on the same page or set of definitions. Of course not every skill depends on linguistic literacy.

Take skateboarding, for example. Yes, there could be some theory, potentially (I'm clearly not a skater) but much of the skill is in learning how to physically operate the board as an extension of one's body. This is a "natural" sort of skill that meshes well with our evolved neurobiology (ie perception, motor function, physical coordination, etc.)

Now, let's look at written language. It is NOT a "natural" sort of skill. It MUST be taught and learned with effort because our neurobiology has not evolved to account for the sorts of tasks involved. Writing is an abstract thing that requires abstract thinking to really understand - the word "lion" is not literally a lion, which is not a simple task to grasp for an untrained brain.

Next, computing. A computer and what it does is incredibly abstract. A bunch of pieces of specially-shaped stone, use an invisible force to represent presence and absence (the concept of "zero" is only in recorded use for the last 3800 years or so and ancient greeks didn't even have a symbol for it). By performing ever more complex mathematics on these stones, we can create tools that people can use to perform abstract, and in some cases, physical work. And these interactions are nearly all performed based upon instructions that people write in text-based languages that don't even match up with natural languages.

Even if not, technically illiterate people can actually read a button or menu item.

And this is part of the origin of the issue inflicted upon younger people. In the US, literacy programs were largely replaced by programs literally designed to help people that are illiterate take care of their basic needs in a society that depends on written language.

Another way of putting it is: An illiterate person can press a button on a touchscreen to order a hamburger, because either there is a symbol of a hamburger, or, they were taught to recognize the shape of the word "hamburger". But, they might not actually know what the price actually means or, they may mistakenly order a plane ticket to Bamberg, Germany, because the words look alike. If they have a computer and an error dialog box pops up, will they know how to figure out how to fix it? Will they install "anti-virus" software that opens in a popup because it looks similar?

How about if they want to learn how to write a resume? How will they do that? What about figuring out how to write a mod for Minecraft? Or Enterprise software? These are all things that are dependent on linguistic literacy. Reduction in the general population's literacy makes people easier marks for cons and significantly reduces their ability to learn new things as well as effectively operate computers for anything but games and scams.

ETA: I'm far from an expert and would really recommend looking into what LeVar Burton of Reading Rainbow and Star Trek fame is saying about this problem.