A Research Study to See How Much CagriSema Lowers Blood Sugar and Body Weight Compared to Placebo in People With Type 2 Diabetes Treated With Once-daily Basal Insulin With or Without Metformin

Inclusion Criteria:

• Male or female (sex at birth).

• Age 18 years or above at the time of signing the informed consent.

• Diagnosed with type 2 diabetes mellitus ≥180 days before screening.

• On stable once-daily dose of basal insulin (minimum of 0.25 units per kilogram perday (U/kg/day) or 20 U/day) alone or in combination with metformin (at effective ormaximum tolerated dose as judged by the investigator) for 90 days prior toscreening.

• Glycated haemoglobin (HbA1c) 7.0-10.5 percent (53-91 millimoles per mole [mmol/mol]) (both inclusive) as determined by central laboratory at screening.

• Body Mass Index (BMI) greater than or equal to 25 kilogram per square meter (kg/m^2)at screening. BMI will be calculated in the electronic case report form (eCRF) basedon height and body weight at screening.

Exclusion Criteria:

• Female who is pregnant, breast-feeding or intends to become pregnant or is ofchildbearing potential and not using a highly effective contraceptive method.

• Renal impairment with estimated Glomerular Filtration Rate (eGFR) less than 30milliliters per minute per 1.73 square meter (mL/min/1.73 m^2) as determined bycentral laboratory at screening.

• Treatment with any medication for the indication of diabetes or obesity other thanstated in the inclusion criteria within 90 days before screening.

• Uncontrolled and potentially unstable diabetic retinopathy or maculopathy. Verifiedby an eye examination performed within 90 days before screening or in the periodbetween screening and randomisation. Pharmacological pupil-dilation is a requirementunless using a digital fundus photography camera specified for non-dilatedexamination.

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

• Recurrent severe hypoglycaemic episodes within the last year as judged by theinvestigator.