I had similar issues when using fbs which uses pyinstaller but older versions.
I recommend installing the pyinstaller and Python like i mentioned here you might be able to get pyinstaller working with later Python 3.7 or 3.8 as they pushed some updates since but i have not setup a new test to see if they play nice like Python 3.6 does
I also have seen alot of people with issues when using anaconda vs standard python install so id recommend trying that too to see if it helps.