In the KiCad project manager, you can: File / New Project from Template, and then choose between two versions of a “hat” for the Raspi.
Also, with: RepoRecon and then fill in “KiCad” for the topic and “description:raspberry”, you get a list of 345 projects related to KiCad and the raspi’s. You can use them as is, as inspiration for derivatives, or just to take some small parts out of for your own projects.