As Wieland said in earlier answer, there's no TensorFlow package in Python 3.9.
So, I felt awkward little bit. If there's no tensorflow package than how can I deal with data science and machine learning. I searched on DuckDuckGo little bit. I found a question similar to this(completely same). There's an answer which said `tf-nightly`(tf=TensorFlow) works in python3.9. He said also. So, I tried
pip3 install tf-nightly
Hopefully, tensorflow is working now....