TwitchIO 2 requires Python 3.7+. You can download the latest version of Python here.
py -3.9 -m pip install -U twitchio
python3.9 -m pip install -U twitchio
Make sure you have the latest version of Python installed, or if you prefer, a Python version of 3.7 or greater.
If you have have any other issues feel free to search for duplicates and then create a new issue on GitHub with as much detail as possible. Including providing the output of pip, your OS details and Python version.