This study will assess the safety, tolerability, the pharmacokinetics from single injection (under the skin) of NNC0581-0001 and explores the pharmacodynamics in healthy participants and participants with hepatic steatosis (increased liver fat). Participants will either get NNC0581-001 or Placebo (dummy treatment). Which treatment participants get is decided by chance.NNC0581-0001 is a new medicine which cannot be prescribed by doctors. The study will last about 58 weeks.

Inclusion Criteria, for healthy participants in Part A:

• Female of non-childbearing potential or male aged 18-55 years (both inclusive) at the time of signing informed consent.
• Body Mass Index (BMI) from 18.5 to 30.0 kilogram per square meter (kg/m^2) (both inclusive) at screening.
• Considered to be generally healthy based on the medical history, physical examination, and the results of vital signs, electrocardiogram, and clinical laboratory tests performed during the screening visit, as judged by the investigator.

Inclusion criteria for participants with hepatic steatosis in Part B:

• Female of non-childbearing potential or male aged 18-55 years (both inclusive) at the time of signing informed consent.
• Body Mass Index (BMI) from 25.0 to 34.9 kilogram per square meter (kg/m^2) (both inclusive) at screening.
• Hepatic steatosis identified by a score above 248 dB/m by Fibroscan® (Controlled Attenuated Parameter, CAP) at screening.

Exclusion Criteria

• Any disorder, which in the investigator's opinion might jeopardise participant's safety or compliance with the protocol.
• For Part A: Any laboratory safety parameters at screening outside the below laboratory ranges, see laboratory provided reference ranges for specific values (re-screening or re-sampling is NOT allowed if the participant has failed one of the exclusion criteria related to laboratory parameters):
• Alanine aminotransferase (ALT) greater than upper normal limit (UNL) plus 10 percent
• Aspartate aminotransferase (AST) greater than UNL plus 10 percent
• Bilirubin greater than UNL plus 10 percent
• Estimated glomerular filtration rate (eGFR) below 90 milliliters per minute per 1.73 square meters (90 mL/min/1.73m^2)
• Glycated haemoglobin (HbA1c) greater than or equal to 5.7 percent (39 millimole per mole [mmol/mol]) at screening.

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.