According to http://pyinstaller.47505.x6.nabble.com/Help-Failed-to-execute-script-td2705.html apparently there is an issue with workalendar's init that makes it incompatible with PyInstaller.

I tried their "very hacky fix" and it works. It would be nice if you could fix your init.

I tried with python 3.9.5 and workalendar 15.3.0.
Thank you in advance.
SD