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 ofscreening.

• 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 anyof the following anti-diabetic drugs or combination regimens:

• Any metformin formulations greater than or equal to (>=) 1500 milligrams (mg) ormaximum tolerated or effective dose.

• Any metformin combination formulation greater than or equal to (>=) 1500 mg ormaximum 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. Verifiedby a fundus examination performed within the past 90 days before screening or in theperiod between screening and randomisation. Pharmacological pupil-dilation is arequirement unless using a digital fundus photography camera specified fornon-dilated examination.

• Potentially missed diagnosis of Type 1 diabetes (T1D) or latent autoimmune diabetesin 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}]) orantibodies to glutamic acid decarboxylase (anti-GAD) greater than 5units/millilitre, as measured by the central laboratory at screening.

• Presence or history of pancreatitis (acute or chronic).

• Renal impairment measured as estimated Glomerular Filtration Rate (eGFR) value ofless than 30 millilitre per minute per 1.73 meter square at screening as defined byKidney Disease: Improving Global Outcomes (KDIGO) 2012 classification.

• Any episodes of diabetic ketoacidosis within 90 days before screening.

• Known hypoglycaemic unawareness as indicated by the investigator according toClarke's questionnaire question 8.