When creating a post, there is a real disconnect between the content of the post and the elements in the sidebar. For this reason, I and am sure others, forget to set a featured image. Features images are useful for list pages like archives and for plugins like yoast to pick the image that best reflects the content. It feels odd that you could have a post with many images, in form of image, cover or gallery blocks and not the correct featured image.

Describe the solution you'd like
Add a button to the image / cover blocks, called "set as featured image". This is just a helper that sets the current image a feature image. It could also save data on block to say it is feature. This could help themes work on the current featured image and stop it being displayed twice at the top of a post.

Describe alternatives you've considered
Add a new feature image block, but this just feels like a copy of the current image / cover blocks.