Taika Waititi discovered in his research that WWII Germany was very vibrant and fashionable and was interested in shying away from traditional war films that presented it as dark and dreary. He opted, instead, to present the city as a celebratory place on the surface and dressed the characters as stylishly as possible. He liked the idea that everything seems happy, but just underneath the surface "the third Reich is crumbling, and, you know, the dream is over."
When Taika Waititi, who is Maori/Jewish, was asked about why he chose to play the role of Adolf Hitler, he said "The answer's simple, what better 'fuck you' to the guy?"
Taika Waititi has known Thomasin McKenzie (Elsa) since she was "very, very little" as he's friends with her parents, from New Zealand's theater scene. He tasked her with watching Heathers (1988) to give her the vibe he was looking for with the character.
Taika Waititi described the film as a love letter to his mother, and single parents everywhere: "It wasn't until I was a grown up and I had kids of my own that I realized 'oh, these parent people, they make a lot of sacrifices, it's really hard raising a kid!'"
One of Taika Waititi's reasons for making the film was the realization that after World War II people cried that "we should never forget," but given the behavior of "certain people in certain parts of the world," it felt to him like we are forgetting.