A Study to Test How Taking BI 1015550 for 12 Weeks Affects Lung Function in People With Idiopathic Pulmonary Fibrosis (IPF)

Inclusion Criteria: 1. Patients aged ≥40 years when signing the informed consent. 2. Diagnosis: 1. IPF based on 2018 ATS/ERS/JRS/ALAT Guideline as confirmed by the investigator based on chest High Resolution Computed Tomography Scan (HRCT) scan taken within 12 months of Visit 1 and if available surgical lung biopsy. and 2. Usual interstitial pneumonia (UIP) or probable UIP HRCT pattern consistent with the clinical diagnosis of IPF, as confirmed by central review prior to Visit 2\* * if indeterminate HRCT finding IPF may be confirmed locally by (historical) biopsy 3. Stable for at least 8 weeks prior to Visit 1. Patients have to be either : * not on therapy with nintedanib or pirfenidone for at least 8 weeks prior to Visit 1 (combination of nintedanib plus pirfenidone not allowed), or * on stable\* therapy with nintedanib or pirfenidone for at least 8 weeks prior to Visit 1 and planning to stay stable on this background therapy after randomisation. \[\*stable therapy is defined as the individually and general tolerated regimen of either pirfenidone or nintedanib\] 4. Forced Vital Capacity (FVC) ≥45% of predicted normal at Visit 1 5. Diffusion capacity of the lung for carbon monoxide (DLCO) (corrected for haemoglobin \[Hb\] \[Visit 1\]) ≥ 25% to \< 80% of predicted normal at Visit 1. 6. Signed and dated written informed consent in accordance with ICH-GCP and local legislation prior to admission to the trial. Exclusion Criteria: 1. Relevant airways obstruction (pre-bronchodilator Forced Expiratory Volume in one second (FEV1)/Forced Vital Capacity (FVC) \< 0.7) at Visit 1. 2. In the opinion of the Investigator, other clinically significant pulmonary abnormalities. 3. Acute IPF exacerbation within 4 months prior to screening and/or during the screening period (investigator-determined). 4. Lower respiratory tract infection requiring antibiotics within 4 weeks prior to Visit 1 and/or during the screening period. 5. Major surgery (major according to the investigator's assessment) performed within 3 months prior to Visit 1 or planned during the course of the trial. (Being on a transplant list is allowed). 6. Any documented active or suspected malignancy or history of malignancy within 5 years prior to Visit 1, except appropriately treated basal cell carcinoma of the skin, "under surveillance" prostate cancer or in situ carcinoma of uterine cervix. 7. Evidence of active infection (chronic or acute) based on clinical exam or laboratory findings at Visit 1 or at Visit 2. 8. Any suicidal behaviour in the past 2 years (i.e. actual attempt, interrupted attempt, aborted attempt, or preparatory acts or behavior). 9. The patient has a confirmed infection with SARS-CoV-2 within the 4 weeks prior to Visit 1 and/or during the screening period. Further exclusion criteria apply.