Welcome to vertical featured image post! The best way to demonstrate a vertical image with your blog post. This theme allows you to add images with flexible height so that you can demonstrate what you want.
The overall concept is very simple, You just need an image with width greater than or equal to 1140px and of any height. When you upload the image as featured image from WordPress post editor, WordPress automatically crop the images to1140px width and proportional height of no matter what value. This way if you upload an image that has more height than width then you end up having a vertical image as featured image. It is that simple.