Additional Study Information: The purpose of this study is to see how teclistamab by itself compares to study treatment combinations that are commonly used to treat multiple myeloma. These study treatment combinations are either pomalidomide, bortezomib and dexamethasone (called PVd) or carfilzomib and dexamethasone (called Kd). The patients will be randomly assigned to on of the study groups. The term "randomized" means something is done by chance or without any particular pattern, like flipping a coin to decide an outcome. The term study drug(s) refers to teclistamab and to the combinations PVd and Kd. Teclistamab, Carfilzomib-dexamethasone (Kd) combination have been approved by the U.S Food and Drug Administration (FDA). However, in this study teclistamab is considered experimental (not FDA approved) because it is being used for adults who have a type of cancer called multiple myeloma that came back or didn't respond to other treatments.