I cannot reproduce your error with a fresh install on Ubuntu 20.04:
docker run --rm -it ubuntu/ubuntu:20.04 /bin/bash

apt-get update && apt-get -y install python3 python3.8-venv

python3 -m venv --system-site-packages ./venv
source ./venv/bin/activate  # sh, bash, or zsh
pip install --upgrade pip
pip install --upgrade tensorflow
python -c "import tensorflow as tf;print(tf.reduce_sum(tf.random.normal([1000, 1000])))"

tf.Tensor(97.31439, shape=(), dtype=float32)