If you have problem with react.
try adding below line to app.js
import "@fortawesome/fontawesome-free/css/all.min.css";
and in package.json add
"@fortawesome/fontawesome-free": "^6.1.1",
(Version doesnt matter add latest)
You should good to go.. More details on, https://fontawesome.com/docs/web/use-with/react/use-with