Just read the doc: https://www.alfredapp.com/help/workflows/inputs/script-filter/json/
It seems that Alfred requires icons to be provided by a file? So it seems that Alfred cannot use Emoji as an icon, or provide icons in BASE64 format? In addition, if using a file as an icon, is there any requirement for the image format? Must it be PNG? Or can it be SVG, JPEG, and so on?