There is a reddit comment from (allegedly) one of the people who worked on the vfx for this film. According to them, the higher-ups insisted on using the real footage, while the artists tried to persuade them to remake those scenes in CGI, and one of the artists even voluntarily took some unpaid overtime to redo those scenes.

If you’re interested, watch the VFX Artists React episode on it, should be the most recent one as of now, there’s more info there