Hi, @painlessseo.
I have accessed the link and watched the introduction video. Indeed the sheet editor plugin allows to edit featured images, but not from the post editor.
If the goal is to set the featured image without a meta box in the post editor, FIFU has multiple ways to do that.
The simplest way would be with our quick editor:
https://ps.w.org/featured-image-from-url/assets/screenshot-6.png?rev=2750395
Accessing /wp-admin/edit.php?post_type=web-story you should see FIFU quick editor, however, that’s not available in our free version.
Let me know if that’s what you were looking for.