A dummy is a door knob or lever that doesn’t turn or have any moving parts. Usually they are used on interior french doors and pantries. They usually need either a spring catch mounted at the top of the door or on the side for single (closet and pantry) doors.
A dummy is about half the price of a regular knob…. because it’s about half the hardware, they are sold singularly, and have no moving parts.
To answer your question, unless your bedroom has french doors on it, you probably can not use a dummy. Even then, usually french doors on bedrooms have normal privacy locks and a latch that secures one of the doors in-place during normal operation.