A significant departure from the TV show is the film's unique structure. Counter to its marketing, the movie is not a full live-action/CG hybrid; the first two-thirds are rendered in the familiar 2D style of the series and its 2004 predecessor. This later part then transitions to a visually striking, blockbuster-style 3D CG world on land. The live-action sequences, featuring Antonio Banderas, were shot in various locations throughout Savannah and Tybee Island, Georgia. The film is also dedicated to Ernest Borgnine, the original voice of Mermaid Man, who passed away in 2012.
I'm assuming LK21 might refer to a specific theater or location where the movie was screened. Unfortunately, I couldn't find any information on LK21 being directly related to the movie's production or distribution. However, it's possible that LK21 was a cinema or a venue that hosted a screening of the film. the spongebob movie sponge out of water lk21