LW, it's pretty obvious. Watch Henry of 2008-2009 to get the basic idea. Pep's wingers are not wingers in traditional sense, they frequently move centrally and, what's important, are not always obliged to track their fullbacks. Mbappe also can play centrally in case Jesus (main 'false9') needs rest.
Guardiola playing 442 is just your fantasy, this formation contradicts the basics of his approach (triangles all over the pitch, using the '3rd man' etc.). The system with wide wingers getting diagonal switches and 'false 9' was used by Cruyff 25-30 years ago, it's not even Pep's invention. Even Begiristain himself played as a winger in the same formation. 3-5-2 is a possibility, but you don't buy young wingers like Sane to rot them on the bench.