Macbeth began filming a couple weeks ago. IMDb has it listed for 2021 but e.g. True Grit started production in March and made Christmas so this easily could as well.
As for Fincher, I mean we know thus far the Oscars have only acknowledged him when he went atypically sentimental and then when he made the single most breathlessly acclaimed American movie in years. Generally his sensibility is too cold and abrasive for them. Mank has a number of advantages on its side but it's by no means locked even if it's quality.