Dim everything except the one part that matters. It stays fully editable: move it, resize it, change how dim it is, or remove it anytime.
Spotlight lives in the More tools tray (⋯, inside the Draw group): an occasional-use tool, one click away. It is the opposite of Black-out box: it hides nothing and deletes nothing, it just fades the surroundings back so one region stands out. Drag a box, everything outside dims.