Creating a React JS progress bar based on progress of Flask microservice?
You have broadly speaking three choices:  

Websockets with flask-websockets
https://flask-socketio.readthedocs.io/en/latest/ 
ServerSentEvents
https://en.wikipedia.org/wiki/Server-sent_events 
Having the process update an in-memory cache that you can poll through another ingress route.

The first and second are difficult if you run Flask properly with WSGI.
I'm trying to create a progress bar in React by calling a Flask microservice with Python.
I don't have problems to display the component in the frontend but I don't know if:

Is possible to get a response with the progress of a script done in a
Flask microservice?
Can a socket communication be established between Javascript and Python?