This study is open to adults with a type of kidney disease called focal segmental glomerulosclerosis (FSGS). The purpose of this study is to find out whether a medicine called BI 764198 improves the health of the kidneys in people with FSGS. Three different doses of BI 764198 are tested in this study.

Participants are put into 4 groups randomly, which means by chance. Three of the groups receive different doses of BI 764198 and one group receives placebo. Participants are in the study for about 4 months. For about 3 months, they take BI 764198 or placebo as capsules once a day.

Placebo capsules look like BI 764198 capsules but do not contain any medicine. Participants visit the study site about 10 times. You can participate in this study from your home. In this case a research nurse will visit you for the study visits.

Kidney health is assessed based on the analysis of urine samples, which participants collect at home. At the end of the study, the results are compared between the different groups. During the study, the doctors also regularly check the general health of the participants.

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.

Once the criteria in section "Time Frame" are fulfilled, researchers can use the following link https://www.mystudywindow.com/msw/datasharing to request access to the clinical study documents regarding this study, and upon a signed "Document Sharing Agreement".

Furthermore, researchers can request access to the clinical study data, for this and other listed studies, after the submission of a research proposal and according to the terms outlined in the website.

After structured results have been posted, all regulatory activities are completed in the US and EU for the product and indication, and after the primary manuscript has been accepted for publication.

For study documents - upon signing of a 'Document Sharing Agreement'. For study data - 1. after the submission and approval of the research proposal (checks will be performed by the sponsor and/or the independent review panel, including checking that the planned analysis does not compete with sponsor's publication plan); 2. and upon signing of a legal agreement.