As many already know, Elementor is very reluctant to stay up-to-date with their CMS. It still uses Font Awesome version 5 and if you don't have a Pro license for Font Awesome, it is very difficult to integrate FA6 as icons.
So to help fellow developers, here is how you can do it!
In Elementor you can import icon sets that are exported by Fontello (as ZIP).
Because Fontello does not support FA6, you have to generate this ZIP file yourself.