Icon dont show in search Icon field

Problem/Motivation

in the filter field the fontawesome icon is not shown, only a box with the code

Steps to reproduce

1. install the composer module require 'drupal/fontawesome:^2.26'.
2. verify loading of css libraries by theme vs 5
3. use

class="fa-solid fa-atlas fa-fw fa-2x" -> class="fa fa-solid fa-atlas fa-fw fa-2x"

the css fa or fas class is missing for the icon to be displayed correctly