Hi gentib,
• Use a fresh new scene. Set the Project> Project Settings> FPS to your liking.
• Then (!) go to the Render Settings> Output> Frame Rate, and set the same FPS there as well.
• When this is done, go to the
Main Menu> Window> Customization> Save As Default Scene
Done.
Every new project file will be like a copy of this “New.c4d” file.
All the best