Hey @weizung -
I use a different method to set up Font Awesome in Sage (which you may have better luck with), but here’s the first thing I’m noticing in your code: the @fortawesome/fontawesome package is deprecated, and you’re mixing it with the newer @fortawesome/fontawesome-free package.
I would recommend heading over to Font Awesome to get clarification on how you would set this up and then trying again once you have a clearer picture of how their packages and config work. If you’re still running into problems that might be connected to Sage after setting up their packages correctly, I can try to help you out here.
Also, FYI, Font Awesome recommends against using pseudo elements with SVG like this. May still work fine for you, but good to know.