As noone had any idea on the SegFault I encountered I found the following: my python3.11 was installed through homebrew. I now installed a python3.11.8 directly from python.org with the provided installer. I was then able (using the erand long paths of this installation) to install pipx and pynitrokey using python3.11.8 and now it's working without errors. My problem obviously was a faulty installation of python3.11 from homebrew ...