I noticed that it's not that easy to write the firmware for the trackball myself, my version was pretty sticky, but it worked. However, that was enough for me to understand the function. Then I have to look for a clever library on the internet, but unfortunately I didn't find any library, but the following brilliant demo code:

https://github.com/LSChyi/blackberry-mini-trackball

The trackball works super smooth now. The rotary encoder with the button and the two mouse buttons were then written fairly quickly.

I will upload the arduino code, all STL's of the case, bash scripts etc. here at the end of the project (hopefully before the cyberdeck contest deadline).

demo of the peripherals arduino