the issue is that the bar_label is a new feature and available in matplotlib version 3.4 or later – ref this link. Check the version of matplotlib using
import matplotlib
print('matplotlib: {}'.format(matplotlib.__version__))
Upgrade to v3.4 or latest version using pip install matplotlib --upgrade. You will need to include the code in the link you provided and as mentioned by JohanC and be able to see bar labels
solved Labeling horizontal bar using matplotlib bar_label [duplicate]