Jette Søndergaard and Peter Hansen Tygesen who play niece and uncle in the movie are in fact niece and uncle in real life.
The first line of dialogue in the movie is heard after 9 minutes, when the uncle says "Nutella" as he and Kris are out grocery shopping.
The director Frelle Petersen met the entire cast of Uncle (2019), during the production of The Art of Crying (2006), while working as assistant director. The Art of Crying (2006) was shot in the same area and same dialect as Uncle (2019).