Mesh
Mesh units pass the Wi-Fi through one house, so you are not stuck with one router in a corner. They help with brick walls, a second storey and a long single building. Each unit still has to reach the last one. Metal, long distance and trees drop that signal quickly.
A wireless bridge
A bridge is a pair of outdoor radios aimed at each other. It is the stand-in for a trench. It does not, by itself, give you Wi-Fi inside the far building. That building still needs an access point, and cameras still need power and a recorder plan.
If the shed, stable or granny flat has no signal, it needs a wireless link to that building, not another Wi-Fi unit inside the house.
A simple way to choose
Same roof, weak rooms: mesh or extra access points. Different building, especially steel: a link, then coverage inside. Both can exist on one property. The house can be meshed and the shed can sit on a bridge.
