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[snippsat]

There is no official support for 3.9 yet.

Requirements and Tested Platforms
Python:
3.5-3.8

tinyaes 1.0+ (only if using bytecode encryption). Instead of installing tinyaes, pip install pyinstaller[encryption] instead.

Try developer version will have earliest support for 3.9

pip install https://github.com/pyinstaller/pyinstaller/archive/develop.tar.gz