In order to integrate React Final Form with a UI component library such as Material UI, you'll need to create a thin wrapper that passes properties between MUI and RFF components. After searching around for who else has done this, you've stumbled across this project.
One thing to note in the demo is the ability to control the react form rendering. This is what really motivated me to go with RFF. With a small configuration tweak to RFF, it is easy to cut the number of renders down to the bare minimum. This improves performance significantly, especially with larger forms.