When I try to use my own version of Fontawesome pro the "duotone" icon type only works if the plugin was initializated by JS.
But in my project i need initialize as CSS.
The JS version working:
The CSS version bug:
This is how Fontawesome Pro Duotone Icons work and we can not control their solutions.
However In the next update(in a few weeks) of Metronic we are releasing our new icon set Keenicons with 670_ icons in 3 styles: Duotone, Outline, and Solid and to use the duotone icons without js and SVG. You can use it as a normal icon as shown below: