There are a few characters from the 1984 film who are not in the 2021 film, including The Emperor and Alia Atreides.
The Emperor is mentioned in the film, and his desire to kill the Atreides is what drives the film’s conflict, but we never actually see him. Alia is technically mentioned when we are told that Lady Jessica is pregnant but at the end of the film she is not born yet. Princess Irulan and Feyd-Rautha (who was played by Sting!) Are not in the new film either. The Emperor, Alia and Irulan are likely to appear in Part 2 – that’s just my assumption, as they’s pretty important in the book – but who knows if we’ll see another rock star embody Feyd.