Gary Oldman wanted to wear elaborate prosthetic makeup to closely resemble the historical Herman J. Mankiewicz but was persuaded otherwise by David Fincher, who wanted minimal makeup for capturing a more intimate performance.
In the scene where Mank visits Irving Thalberg, Thalberg briefly alerts his secretary to never allow the Marx brothers in his office again. This is because Thalberg would often postpone and even leave meetings early with the brothers, much to their annoyance. In retaliation, when Thalberg returned one time for a meeting with them, he found the Marx brothers completely naked in his secretary's office, roasting potatoes by the fireplace. This is also why Mank notes the office smells like summer.
Mank (2020) has a monaural sound mix, similar to what films had before the stereophonic sound system was introduced in the mid-20th century. This means that instead of multiple soundtracks dedicated to dialogue, music, and other sound effects, all of the aforementioned were shared on one single track.
Shot on RED's Helium Monochrome 8K cameras, no color version of this film exists.