They had that some time ago somewhat implicitly. Users were able to subscribe to their friends posts based on post type (image, text, link, etc.) Back then I

They had that some time ago somewhat implicitly. Users were able to subscribe to their friends posts based on post type (image, text, link, etc.) Back then I was an active Facebook user and selected to subscribe only to image content. It worked great for a while but got obsolete both by Facebook removing those subscription options and (earlier) the users emerging habit to add pictures to every post to increase reach, no matter the content.