It seems like you are using Tensorflow 1 with the highest Keras version.

Follow Keras announcement on their GitHub. Try to downgrade Keras’s version to 2.2.5 or lower for Tensorflow 1 and 2.4.0 for Tensorflow 2.

However, if you want to use Tensorflow 2, they recommend using Keras in Tensorflow which is updated frequently (Check there Github: https://github.com/tensorflow/tensorflow/tree/master/tensorflow/python/keras)