I kinda feel like there is a fair amount of authors in post-D&D fantasy lit who approach magic as if they were engineers, and a fair amount of that magic also involves blasting as if they were playing wargames. In contrast, I would say that Le Guin approaches magic in Earthsea as a philosopher, teacher, or sage interested in teaching the Tao/Dao.
I feel like Le Guin sites her magic in words, which maps to the act of writing itself. Bringing the land out of the sea with one word, giving it form, and reforming it, with others. It ties closely to what has been discussed over the last few pages of this thread: the relationship of signifiers to signified. As an aside, the College of Naming Incantations in SPIs DragonQuest attempted to work naming into a TTRPG system. Another attempt was Truenamer in Tome of Magic for D&D 3e. Both seem to anchor around a notion of naming as power to find, call and control, although namers in DQ also have a special power to counter spells.
D&D has from the start had a technological (or as you say, engineering) approach to magic. One might not like the dressing, but it is ignoring the game texts to say that it does not have rules for what you can do, how you can do it, and its effects.
When it comes to pretending that something false is true, I feel like one has to admit the reality of the signifier. When I refer to a
golden mountain, one thing I am confident about is that the
signifier has mental and (here) digital standing. Shared norms about gold and mountains mean that with less confidence I know that features of what you and I picture to be signified have probabilities of correspondence. Such features include ideas about what one may do with, to or on a golden mountain.
Some arguments appear to some extent to ask me to commit to polarities, slippery slopes or binaries. All or nothing. While experienced play with signifiers whose signified I am able to form and sustain pretences about and share those with others occurs where it can. It tolerates and has means to repair ambiguities.
I may not be able to imagine something eleven dimensional, but just because I can't imagine something eleven dimensional doesn't mean that I can't imagine something I'm familiar with, like a blue enamel cup. I observe TTRPG conversations occurring in a space of signifiers that are normally imaginable. Referring to the point made up thread about authority, I feel there is a significant element of being queryable. Signifiers in play aren't static... we add to them what we need. "How high is the mountain" "1000 feet" "Does anything live on it?" "Lichen" and so on. I keep coming back to my earlier proposal
I would then regard elements of fiction objectively "real" (to me) just so long as they are decided by someone or some process external to me. Then as you say, there would be facts that I can learn about those objects: they're true just because the person or processes appointed to determine them did so... with the additional qualifier that they must be external to me. And so I can make enquiries about them.
What actually is real is of course not the fictional object, but the decider of facts about that object. That the decide is external to me results in the object not being determined by me, which I can pretend to appreciate in the way I experience real (no quotes) objects like tables and chairs.
And to me this in some way contrasts with authority. There's an idea that you could own all rights to say things about mountains in our game, but this can be analyzed further. Broken into "exclusive right to describe" and "the job of describing". I can serve other players by accepting the job of describing without that being an exclusive authority thing. Or I can own the thing (my character is a great example) and no one else is allowed to describe that thing. I can even move between the job of describing (for myself) and the job of working with what was described.
Finally (for this post!) I feel that our experience of the world itself is not a firm one. In pretending something false is true, I am not straying so far from pretending that places I've never been, never seen pictured, read only as a name on a map, exist. I'm not straying so far from the fact that I must rely on my senses, seeing in twilight a creature crouching in the shadows... that is not really there. The world is not so substantial and our pretend world not so insubstantial, as to prevent me imagining one is the other.