Hi Matthias, shouldn't the severity be "important" if the FTBFS is really related to python 3.9 until this version becomes the default python version?
AFAICS 3.8 is still the default, here [1] it is not yet listed for bullseye, and ITK is build only against the default python version (everything else would be insane regarding the build time and the disk space needed for building the package). If you don't object I'll now check whether the configuration error also occurs with 3.8 and lower the severity if there are no problems. Best, Gert [1] https://wiki.debian.org/Python#Supported_Python_Versions
