A Washington Post article titled "Budgets for 'prestige' films dried up. So Ava DuVernay found a new way." was released on 12/4/23; it details how DuVernay financed the film partly through grants, including from the Ford Foundation, which enabled her to make a bigger film.
According to DuVernay in her interview at Columbia Journalism School, the actor describing the pool scene is a background actor who had been through a similar experience in real life. The scene was altered so he paraphrased the script events drawing on the emotion from his own lived experience. The script originally had the narration being done by Isabelle Wilkerson (Aunjanue Ellis-Taylor).