If you choose a number the module will give you this error (for example "1"):
Invalid icon name 1. Please see the Font Awesome icon list for correct icon names, or turn off validation in the Font Awesome settings if you are trying to use custom icon names.
This is because it has been using strict comparison:
https://git.drupalcode.org/project/fontawesome/-/blob/8.x-2.x/src/FontAw...
$findIcon is a string("1") and $icon['name'] is a number(1).
Needs review
2.0
Code