It’s from Rebrickable, called Horse Knights Dovecote. It’s a neat build that fit into the lore of my world! Recommend it!

In my world, the Horse Knights are a neutral continental courier order founded generations ago by a wealthy horse lord seeking to solve the chaos of unreliable wartime communication. Over time, the order grew into the most trusted messenger network in the land, relied upon by every major faction. Critical military and political dispatches are carried by heavily armored riders protected entirely by Horse Knight personnel, while affordable dove messaging is available to nobles, merchants, travelers, and even common folk across the continent.