This one is doing the job and it optionally loads Font Awesome on back-end or front-end -

https://wordpress.org/plugins/block-for-font-awesome/

I do think that a rich-text option is good, though, as since the block editor, nothing can be added inline. If I can't rely on the plugin above for various reasons, I insert the Font Awesome SVG via HTML mode. It takes a bit of time, but it's worth it from a performance point of view.