H.P. Lovecraft put his works into the public domain before his death, but even if he hadn’t enough time has passed that those works would have entered the public domain anyway. That’s why anybody can, and pretty much everybody has, done their own thing with Cthulhu and the larger Lovecraft mythos. Sam Raimi made full use of the Necronomicon from Lovecraft’s oeuvre, making it the star, alongside Bruce Campbell as ash, of his EVIL DEAD series of films. (And now that Ash is retired—and of this Mr. Campbell is adamant—and the movies are continuing without him, the Necronomicon will have the spotlight to itself.) Marvel Comics *could* have used the Necronomicon. Instead they changed the name of the book to the Darkhold, probably so they could do their own thing with it and not worry about deviating too far from Lovecraft’s original take. (Marvel also changed Cthulhu’s name to Cthon and had him appear numerous times in the comics as a non-tentacled non-giant cephalopod. (And there’s no reason why Chtulhu/Cthon *couldn’t* appear as a human if he wanted to.)
Don’t be confused, though. The book that has (SPOILER WARNING) corrupted Wanda Maximov in DOCTOR STRANGE IN THE MULTIVERSE OF MADNESS and turned her into the (sorta) sinister Scarlet Witch is in fact the Necronomicon.
I was so disappointed that, when Doctor Strange got his hands on the tome in the movie, he didn’t first mutter the incantation “Klaatu, barada, nikto!”