What do you call this part of old windows? [duplicate]
Those are shutters:
Each of a pair of hinged panels, often louvered, fixed inside or outside a window that can be closed for security or privacy or to keep out light. — Lexico
Many modern homes have external shutters but I’ve never seen them closed (if they can be — I suspect many are just decorative).
See also 9 Types of Shutters to Know (Interior & Exterior)