The issue was the python version, annotald requires 2.7, but I have default python3.
In case someone needs it, my solution:
install a virtual environment with the 2.7 version of python in a specific directory of your choice with the module virtualenv (see https://virtualenv.pypa.io/en/latest/)
activate the 2.7 venv in the directory of your choice.
install annotald in the 2.7 venv.
on terminal use the following command: <path of the annotald executable (in the bin of the venv)> <path of the .psd file you want to modify>
I am on a mac (Catalina 10.15.5)
I have annotald installed in my project venv.
the exec is here: .../venv/bin/annotald
the packages are here: .../venv/lib/python3.8/site-packages/annotald
When I launch the exec, the following ImportError is given (the error happens when processing line 14 of the annotald exec):
ImportError: No module named annotald.treedrawing
I have the same error when I install annotald in my "regular" python folder (with the same internal setup)