I think a lot of the problem with this movie is that it was touted as a biopic that would show the "true" Marylin Monroe. When in reality this entire movie and the book it's based on is just a perverse, exploitative fanfic.
Marylin Monroe was exploited so much during her life doing decades after her death just seems cruel. She more than just a sex-symbol, tortured artist type. She was human. We barely get to see that her real name was Norma Jean. That she was only Marylin when she needed to be. She may have used Marylin as an escape from past traumas and what not but she was in touch with herself so much that she was able to separate the two lives.
Ana de Armas' acting was not bad by any means. The pacing, dialogue, cinematography were a bit strange but that felt intentional. With so many famous Hollywood stories being retold i think this one was a flop.