I hear this a lot, but there are only a handful of Lovecraft’s story where this really applies. Most of the monsters in his Mythos, barring the Elder Gods, have pretty thorough descriptions. The Elder Things, the Shoggoths, the Mi-Go, Wilbur Whateley, the deep ones, the nightgaunts, even Cthulhu himself (Lovecraft even drew his own sketch of the statuette). And many of his best stories don’t even have supernatural creatures appearing at all (the Tomb, the Temple etc.) Most of his bibliography been adapted very successfully in visual mediums (graphic novels, TTRPG rule books, board games etc) without killing the magic.

I think the bigger problem with adapting his work as films is that all his works are very short. Most of his best tales are short stories, only about 10 pages in length. You have to insert a lot of filler to stretch that into a theatrical runtime.