A Study to Test BI 764198 in People With a Type of Kidney Disease Called Focal Segmental Glomerulosclerosis

Inclusion criteria: * Male and female patients 18 years to 75 years (both inclusive) of age on the day of signing informed consent. * Patients diagnosed with biopsy proven primary Focal Segmental Glomerulosclerosis (FSGS) or documented Transient Receptor Potential Cation subfamily C Member 6 (TRPC6) gene mutation causing FSGS prior to screening visit. * Urine Protein-Creatinine Ratio (UPCR) ≥ 1000 mg/g based on first morning void urine sample during screening. * Patients treated with corticosteroids must be on a stable dose for at least 4 weeks prior to screening visit with no plan to change the dose until end of trial treatment. * Patients treated with Angiotensin Converting Enzyme (ACE) inhibitors, Angiotensin II Receptor Blockers (ARBs), finerenone, aldosterone inhibitors, or Sodium-Glucose Cotransporter-2 (SGLT2) inhibitors should be on a stable dose for at least 4 weeks prior to screening visit with no plan to change the dose until end of trial treatment. * Body Mass Index (BMI) of ≤ 40 kg/m² at screening visit. * Women of childbearing potential (WOCBP) must be willing and able to use highly effective methods of birth control per ICH M3 (R2) that result in a low failure rate of less than 1% per year when used consistently and correctly. A list of contraception methods meeting these criteria is provided in the informed consent form (ICF) and in the study protocol. Further inclusion criteria apply. Exclusion criteria: * Known monogenic (with the exception of TRPC6 gene mutations) or clinical or histologic evidence of secondary FSGS. * Documented Alport syndrome, Nail Patella syndrome, diabetic nephropathy, Immunoglobulin A (IgA)-nephropathy, lupus nephritis, or monoclonal gammopathy (e.g., multiple myeloma). * Concomitant use of calcineurin inhibitors. * Concomitant treatment with cytotoxic agents (cyclophosphamide, chlorambucil), or CD20 monoclonal antibody, e.g., rituximab, within 5 half-lives before screening visit. Note: use of other immunosuppression therapies considered as standard of care may be allowed as long as the patient remains on stable dose throughout the study. * Estimated glomerular filtration rate (eGFR) \< 30 mL/min/1.73 m² at screening visit. * Time between start of the Q-wave and end of the T-wave in an electrocardiogram interval corrected for heart rate (QTc) intervals (QT interval corrected for heart rate using the method of Fridericia - QTcF) greater than 450 ms in males or greater than 470 ms in females, or any other clinically relevant electrocardiogram (ECG) findings (at the investigator's discretion) at screening visit. * Detection of graded cataract by Lens Opacities Classification System III (LOCS III) higher than NC1/NO1, C0, P0 in the slit lamp eye examination at screening visit. Planned cataract surgery during participation in the study. Patients with cataract who have undergone lens replacement are not excluded. * Women who are pregnant, nursing, or who plan to become pregnant while in the study. Further exclusion criteria apply.