The librarypyinstxtractor used here is outdated, so it doesn't apply to the new version of Python 3 (like 3.8).
I just downloaded the latest one fromextremecoders-re/pyinstxtractor: PyInstaller Extractor.
Usage:
python pyinstxtractor.py Example.exe
uncompyle6 .\Example_extracted\Example.pyc > Example.py
And it works fine for me.