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:

1. Diagnosed with Type 2 Diabetes Mellitus (T2D) mellitus greater than or equal to (>=) 180 days before screening.
2. Glycated haemoglobin (HbA1c) of 7-9 percentage [(53-75 millimoles per mole (mmol/mol)] (both inclusive) as assessed by central laboratory on the day of screening.
3. Body mass index (BMI) greater than or equal to (>=) 25 kilograms per meter square (kg/m^2) on the day of screening.
4. Stable daily dose(s) greater than or equal to (>=) 90 days before screening of any of the following anti-diabetic drugs or combination regimens:
5. Any metformin formulations greater than or equal to (>=) 1500 milligrams (mg) or maximum tolerated or effective dose.
6. 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:

1. 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. Pharmacological pupil-dilation is a requirement unless using a digital fundus photography camera specified for non-dilated examination.
2. Potentially missed diagnosis of Type 1 diabetes (T1D) or latent autoimmune diabetes in adults (LADA) verified by C-peptide less than 0.26 nanomoles per litre (nmol/L) (or 260 picomoles per liter [pmol/L] [0.78 nanograms per millilitre {ng/mL}]) or antibodies to glutamic acid decarboxylase (anti-GAD) greater than 5 units/millilitre, as measured by the central laboratory at screening.
3. Presence or history of pancreatitis (acute or chronic).
4. Renal impairment measured as estimated Glomerular Filtration Rate (eGFR) value of less than 30 millilitre per minute per 1.73 meter square at screening as defined by Kidney Disease: Improving Global Outcomes (KDIGO) 2012 classification.
5. Any episodes of diabetic ketoacidosis within 90 days before screening.
6. Known hypoglycaemic unawareness as indicated by the investigator according to Clarke's questionnaire question 8.