Thanks a lot for the link. I followed the suggestion there to build the kivy hello-world-example (with the given main.py file).
I did this by first setting up a new user on my Linux PC (current Debian 12(.5 I think)) with the standard skeleton files (.bashrc and so on).
I ssh'ed into this account.
Than created an virtual environment:
python -m venv --prompt bd ~/.venvs/buildozer
source .venvs/buildozer/bin/activate
pip3 install kivy buildozer cython
buildozer init
edited buildozer.spec such that
android.api = 31
no other changes whatsoever.
than run
buildozer android debug
but the __GNUC_PREREQ problems remains. I also tried with different cython versions from 0.29.15 to 3.0.10 but without success. The old versions produce other errors but the more recent ones always complain about the __GNUC_PREREQ thing.
I am really puzzled as I followed the instructions closely.