This study will look at how much cagrilintide helps people with overweight or obesity and type 2 diabetes lower their body weight. Cagrilintide is a new investigational medicine. Doctors may not yet prescribe cagrilintide. Participant will either get cagrilintide or placebo. Which treatment participant get is decided by chance. Participants are two times more likely to get cagrilintide than placebo. Like all medicines, the study medicine may have side effects. For each participant, the study will last for about 1 year and 6 months.