A Study to Test How Well Different Doses of BI 764532 Are Tolerated by People With a Tumour in the Brain That is Positive for DLL3

Inclusion Criteria: 1. Male or female participants ≥18 years old and at least at the legal age of consent in countries where it is greater than 18 years at the time of signature of the first informed consent form (ICF1). 2. Signed and dated written informed consent (ICF1 and ICF2) in accordance with International Council for Harmonisation-Good clinical practice (ICH-GCP) and local legislation prior to admission to the trial. 3. Patients with histologically confirmed primary progressive diffuse glioma who have failed standard of care therapies. 4. Availability of archival tumour tissue for Delta-like 3 (DLL3) expression. 5. Tumours must be positive for DLL3 expression by immunohistochemistry (IHC) on archived tumour tissue according to central pathology review. 6. Documented unequivocal progression after radiotherapy and/or chemotherapy with measurable disease by response assessment in neuro-oncology (RANO) criteria. 7. Karnofsky performance score ≥70. Further inclusion criteria apply. Exclusion Criteria: 1. Previous treatment in this trial. 2. Current enrolment in another investigational device or drug trial. 3. Presence of extracranial metastatic or leptomeningeal disease. 4. Previous treatment with therapies targeting DLL3. 5. Prior treatment with bevacizumab or other anti-vascular endothelial growth factor (anti-VEGF) or anti-angiogenic treatment within 6 months prior to first administration of BI 764532. 6. Recent anti-cancer therapy: treatment with any other anticancer drug within 21 days or within 5 half-life periods (whichever is shorter) prior to first administration of BI 764532. 7. Radiotherapy within the 3 months prior to the diagnosis of progression; unless tumour progression is clearly outside the radiation field or tumour progression is unequivocally proven by surgery/biopsy. Further exclusion criteria apply.