A Research Study to Look Into How Semaglutide, Together With a Lower Dose of Insulin Glargine, Compares to a Higher Dose of Insulin Glargine Alone in People With Type 2 Diabetes (SUSTAIN OPTIMIZE)

Inclusion Criteria: * Diagnosed with Type 2 Diabetes Mellitus (T2D) mellitus greater than or equal to (\>=) 180 days before screening. * Glycated haemoglobin (HbA1c) of 7-10 percentage \[(53-86 millimoles per mole (mmol/mol)\] (both inclusive) as assessed by central laboratory on the day of screening. * Body mass index (BMI) greater than or equal to (\>=) 25 kilograms per meter square (kg/m\^2) on the day of screening. * Stable daily dose(s) greater than or equal to (\>=) 90 days before screening of any of the following anti-diabetic drugs or combination regimens: * Any metformin formulations greater than or equal to (\>=) 1500 milligrams (mg) or maximum tolerated or effective dose. * Any metformin combination formulation greater than or equal to (\>=) 1500 mg or maximum tolerated or effective dose. The treatment can be with or without sodium glucose cotransporter 2 (SGLT-2) inhibitors. • Treated with a once daily basal insulin (e.g. insulin glargine Unit 100 or U300, neutral protamine hagedorn (NPH) insulin, insulin detemir, insulin degludec) less than or equal to (\<=) 40 units/day (U/day) for greater than or equal to (\>=) 90 days before screening. Short-term bolus insulin treatment for a maximum of 14 days before screening is allowed. Exclusion Criteria: * Uncontrolled and potentially unstable diabetic retinopathy or maculopathy. Verified by a fundus examination performed within the past 90 days before screening or in the period between screening and randomisation. P…