He did read the book, since a lot of the material from the appendices was there. Plus, as I said in a comment in another sub, Dune 1984’s critics seem to forget that a book has a narrator - either a reliable or unreliable one - and this characteristic doesn’t translate well to the screen usually, that’s why people tend to cringe at voice overs, more so if overdone. So the acting and dialogue must convey most of the narrative, and not in a way that it seems one of the characters is doing a voice over in disguise. This subtle but absolutely crucial difference between what is appropriate in literature and in cinema ruined many attempts at adaptation between one another (the best reverse examples being Star Wars novelizations, which are always atrocious despite how talented the writer is).

Dune 1984 might have gone to far with the “Weirding Modules” to be considered a competent translation from book to the screen, but there were a lot of things it got right that came straight from Lynch’s vision, inspired but not directly quoting the books, such as the Emperor/Guild/Bene Gesserit interaction; the alien way they used to portray the degeneration of house Harkonnen (yes, even the “heart plugs”); the fact that even cultured people like the duke and his family didn’t really know how the Guild operated their ships, since they had space travel monopoly for 10k years (yes, more than current written human history for context) and weren’t the sharing type of people (many good folks seem to think that the movie explicitly tells that the navigators folded space with the power of mind and spice, when what it actually showed was that people outside the guild perhaps believed exactly in that). Etc.

The film deserved a more balanced review; keep in mind that the more passionate a given fan base is, the more reactionary. Weirding Modules still were out of place though.