One of Superman’s known weaknesses, besides that of kryptonite, is that he’s as vulnerable to magic as the average human (besides what he can avoid with his super-reflexes).

So why doesn’t he learn to use magic? His Super-intelligence and speed would make it much easier for him to learn magic compared to the average person, and he’s already well aware that magic exists.

Knowing magic would help him cover a major weakness of his, so it seems illogical that he doesn’t pick it up, or look into it.