The class prefixed
fa- is the native way of adding FontAwesome icon on your page. Unfortunately, this is not going to work inside the theme unless you integrity the FontAwesome manually, but you do not need to do that because FontAwesome is already integrated into the theme.
As you know the theme use:
data-x-icon-b for social icons.
data-x-icon-o for outline icons.
data-x-icon-s for solid icons.
Read more about that here, (see the answer under Why are some of my icons are appearing as an empty square?)
Now, if you just want to insert icons on text element, you don't need to do that
data-x-icon thing, you just need to copy and paste a shortcode we provided here.
Hope it helps,