According to director Charlie Kaufman, Netflix pushed back against the film's 1.37:1 aspect ratio because they were concerned that viewers would think there was something wrong with their TV.
The young woman's critique of A Woman Under the Influence (1974) is taken verbatim from film critic Pauline Kael's review of the movie. Earlier in the film, a copy of Kael's review collection For Keeps can be seen in Jake's childhood bedroom (though ironically, that particular review does not appear in that book).
Brie Larson was originally cast before being replaced by Jessie Buckley. Larson had to step down to focus on Captain Marvel (2019) and Avengers: Endgame (2019).
One of the wigs Toni Collette wears for her role was originally made for Stranger Things (serving as the wig the boys put on Eleven in the first season). It was modified for Collette. The same wig was used on Blythe Danner in Madoff.
In an interview, Jessie Buckley stated that, when she received the script, Charlie Kaufman described her character (The Young Woman) as "molecular."