Embedded python fails to compile on Raspberry Pi

[tryfon]

OK, problem solved. It seems that the behavior of the python3-config script was changed in Python 3.8: https://docs.python.org/3/whatsnew/3.8.h...ease-build

To embed Python into an application, a new --embed option must be passed to python3-config --libs --embed to get -lpython3.8 (link the application to libpython). To support both 3.8 and older, try python3-config --libs --embed first and fallback to python3-config --libs (without --embed) if the previous command fails.

So I changed the linker command to
gcc test.o -L/usr/local/opt/python-3.9.1/lib/python3.9/config-3.9-arm-linux-gnueabihf -L/usr/local/opt/python-3.9.1/lib -lcrypt -lpthread -ldl -lutil -lm -lpython3.9 -o test

and it finally worked! Thanks a lot everyone!