A Featured Block Shortcode is a block that has a unique style in every theme, and is meant to highlight some content that you have. It is usually styled to correspond theme design, and its appearance may differ significantly from theme to theme.
You can add all sorts of content inside of this block like images, text of various formatting, media, links etc.
Whatever the Featured Block is styled like, there is always an option of adding a button to it:
Yet, in some themes, a Featured Block shortocode has some additional features, like block color choice and/or button icon direction choice: