Thanks for the fast reply! I already archived all my image, audio and rpy files, but the number of files barely changes.
Even my test project with no assets at all suddenly has more than 1.800 files...
After extracting the .zip folder of my test project "Testing" (2 lines of dialogue, no images, no audio), I get these folders: game (93 files), lib (566 files), renpy (465 files) and Testing.app (538 files). This project hits the file limit even though it has no content.