This is a study to investigate the effect of AZD0780 tablets on low density lipoprotein cholesterol levels (LDL-C) compared with placebo tablets administered in combination with rosuvastatin tablets in adult Russian participants with dyslipidaemia. AZD0780 is a small molecule that reduces the amount of LDL-C in the blood. Placebo will be used for comparison, and neither the participants nor the Investigators will know who is receiving the AZD0780 medication and who is receiving the placebo until the end of study. The total length of the study for an individual participant will be up to 136 days, including a screening period of up to 14 days, rosuvastatin run-in period of 28 days, treatment with AZD0780 or placebo for 84 days, and a safety follow-up period of 10 days.