This study is testing a new medicine that might help treat people with type 2 diabetes. The purpose of the study is to see if the new study medicine is safe and how well is tolerated by the body. There will be two groups of participants in this study: healthy participants and participants with type 2 diabetes. Participant will either get study medicine (NNC1679-0001) or placebo (a treatment that has no active medicine in it). NNC1679-0001 is a new experimental medicine that doctors cannot prescribe yet. Which treatment the participant gets is decided by chance. Participant will get one dose which will be injected into the area around abdomen (belly) by the medical staff.

Inclusion Criteria:

All participants

• Informed consent obtained before any study-related activities. Study-related activities are any procedures that are carried out as part of the study, including activities to determine eligibility for the study.
• Male or female (sex at birth) of nonchildbearing potential.
• Age 18-64 years (both inclusive) at the time of signing the informed consent.

Healthy participants

• Body mass index (BMI) 18.5-29.9 kilograms per square meter (kg/m^2) (both inclusive) at screening.
• Glycated haemoglobin (HbA1c) lesser than or equal to (<=) 6.4 percent (%) (47 [millimoles per mole] mmol/mol) at screening.
• Considered to be generally healthy based on the medical history, physical examination, and the results of vital signs, electrocardiograms (ECG), and clinical laboratory tests performed during the screening visit, as judged by the investigator.

Participants with Type 2 Diabetes Mellitus (T2DM)

• BMI 20.0-34.9 kg/m^2 (both inclusive) at screening.
• HbA1c 6.5-9.0% (47.5-74.9 mmol/mol) at screening.
• Diagnosed with T2DM greater than or equal to (>=)180 days before screening.
• Stable (as judged by the investigator) daily dose(s) of metformin or combination of metformin and dipeptidyl peptidase IV (DPP-4) inhibitors and/or sodium-glucose co-transport 2 SGLT 2) inhibitors >= 90 days before screening.

Exclusion Criteria:

All participants

• Screening alanine aminotransferase (ALT) values greater than (>) upper limit of normal (ULN) +10%, aspartate aminotransferase (AST) values >ULN +20%, or total bilirubin >ULN.
• Renal impairment, defined as estimated glomerular filtration rate (eGFR) <60.0 milliliter per minute per 1.73 square meter (mL/min/1.73m^2), at screening.
• Clinical evidence of chronic kidney disease (CKD) and/or urinary albumin: creatinine ratio (UACR) >30 milligrams per gram (mg/g).
• Presence or history of cardiovascular disease, including stable and unstable angina pectoris, myocardial infarction, transient ischaemic attack, stroke, cardiac decompensation, clinically significant arrhythmias, or clinically significant conduction disorders.

Healthy participants

• Any disorder that, in the investigator's opinion, might jeopardise participants' safety or compliance with the protocol.
• Supine blood pressure at screening outside the range of 90-139 millimeters of mercury (mmHg) for systolic or 50-89 mmHg for diastolic.

Participants with T2DM

• Any disorder except for mild conditions under stable treatment associated with T2DM, which in the investigator's opinion might jeopardise participant safety or compliance with the protocol.
• Supine blood pressure at screening outside the range of 90-159 mmHg for systolic or 50-99 mmHg for diastolic. This exclusion criterion also pertains to those participants who are receiving antihypertensive treatment.

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com.

Sponsor staff involved in the clinical trial is masked according to company standard procedures.