Deke Parsons’s review published on Letterboxd:
At it’s worst, Mank is the Oscar-bait Solo: it answers questions about Citizen Kane that nobody had. At least, I didn’t. I like Citizen Kane, it’s one of the relatively few “great films” that I personally think is great. However, I cared about almost nothing that happened in Mank which centered around Citizen Kane’s creation.
Partly, I think this is because I don’t believe that Mank wrote Citizen Kane alone. It seems much more likely that Orson Welles used Mank to produce the rough draft of the script because Mank had been a dinner guest of Hearst and Marion Davies. I’m not sure why he would have needed a barely-functioning alcoholic already started on his downward spiral, otherwise. Welles obviously has a singular vision for Kane which he could not have just lifted from another man’s screenplay. This, along with the likelihood that Welles’ ego would not have allowed him to use someone else’s script without massively altering it, leads me to believe that there was probably more Welles in the final screenplay than Mank.
There’s also the matter that, Mankiewicz, as portrayed in this film, is a solidly unlikable character. He’s a drunk who emotionally abuses his assistant and his wife, and abandoned his family. He’s rude to everyone. Sometimes powerful people are amused by this for a time, but eventually, they get sick of it, and stop helping his career. This doesn’t make him a martyr, he wasn’t blacklisted—he was an alcoholic. I’m also not sure how Welles harmed him: Welles apparently wanted sole credit for the screenplay, but he didn’t get it. So...why does anyone care about this 80 years later?
It’s watchable, Gary Oldman is good—but, why is this a movie. Because David Fincher wanted it to be. How Wellesian.