Although Dafoe himself is still not officially confirmed to appear in the film, that is definitely the Dafoe version of Green Goblin on the poster.
Sony and Marvel are treating Spider-Man: No Way Home with a level of secrecy typically reserved for, like, classified national security secrets.
He’s not very big, but you can see the Goblin in the poster below in the middle right, just behind that big lightning bolt.
If you’re gonna have this Sam Raimi Green Goblin in the movie, you gotta have at least some of Willem Dafoe screaming “BACK TO FORMULA!” and grimacing like a madman and such.