Making Magic Magical
Lots of writing tends to take the wonder out of magic by explaining the rules too much or making it work like modern day devices. This is my ideas on how to make magic feel magical for your audience.
1. Don't Have Perspective Characters Who Can Use Magic
We see this a lot in the Conan stories. Since Conan is a Barbarian with little knowledge of magic and often a fear of it, it is portrayed as unknowable. This results in magic feeling mysterious and strange. This feeling adds to the stories making them feel more weird and wonderful. This even happens when describing things that we know day to day such as elephants in the Tower of the Elephant story, because Conan does not know what an elephant is he sees it as some mysterious being.
Conan stared aghast; the image had the body of a man, naked, and green in color; but the head was one of nightmare and madness. Too large for the human body, it had no attributes of humanity. Conan stared at the wide flaring ears, the curling proboscis, on either side of which stood white tusks tipped with round golden balls ... This then, was the reason for the name, the Tower of the Elephant.`
The Edge Chronicles especially Beyond the Deepwoods are another great example of this. Rook ventures out into a world unknown for the first time and everything feels magical to him.
Although I love Brandon Sanderson he almost does the opposite of this making all of his magic systems have clear rules that the audience is told. He often has perspective characters who are magic uses and lay out the rules in their thoughts. This isn't always bad but it does take the mystery away.
2. Make Magic Unpredictable
I think magic should still have some rules for internal consistency in your story or world. The audience doesn't need to know these rules though. This works even better when the audience feels like the magical aspects of the world are unknowable. Things like wild magic that when unpracticed causes unusual results or magic that can be misinterpreted add to this feeling.
Having unpredictability on top of not having perspective characters creates a compound effect where magic is this unknown thing that doesn't do what you want. Building on this and then having people fear this unknown and unpredictable thing, or at least be anxious around it, creates a tension around using magical items and abilities. This can allow your characters reason to avoid magic and never truly know it instead of experimenting with it and making it a science. Like often happens in my TTRPG games.