Now you can find a class called:
fa--custom
To control the custom animation you can use the variable:
var(--fa-scroll--custom)
This variable returns values from 0 to 1, the value will also depend on the modifiers.
This opens up the possibilities to use various animations with transforms, e.g:
transform: translateX(calc(var(--fa-scroll--custom) * -100%)) scale(var(--fa-scroll--custom))