A Study to Determine How BI 907828 (Brigimadlin) is Taken up in the Tumor (Phase 0) and to Determine the Highest Dose of BI 907828 (Brigimadlin) That Could be Tolerated (Phase 1a) in Combination With Radiation Therapy in People With a Brain Tumor Called Glioblastoma

Inclusion criteria * Inclusion criteria Part Phase 0: * Histologically (if prior biopsy) or radiologically diagnosed glioblastoma. * Neurosurgical tumor resection is indicated and planned according to the assessment of the treating physician. * Patients must be at least 18 years old. * Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1 (an ECOG of 2 is acceptable, if it is due to non-cancer-related disability, and after agreement with the sponsor). * Inclusion criteria Part Phase Ia: * Histologically demonstrated diagnosis of TP53 wild type glioblastoma harboring unmethylated O6-methylguanine-DNA-methyltransferase (MGMT) promoters. Glioblastoma definition according to 2021 World Health Organization (WHO) Classification of Central Nervous System (CNS) tumors, i.e. IDH- wild type only. * Patient has undergone neurosurgical tumor resection and is eligible for standard radiotherapy. * Patients must be neurologically stable based on the judgement of the treating physician. The use of corticosteroids and anti-seizure medication is allowed and should be at a stable or decreasing dose for at least 7 days before inclusion in the trial. Anti-seizure medication should not include agents that interact with BI 907828 (Brigimadlin). * For patients, who have participated in Phase 0, the interval between the single dose of BI 907828 (Brigimadlin) and subsequent Phase 1a treatment must be at least 21 days. Further inclusion criteria applies. Exclusion criteria * Exclusion criteria Part Phase 0: * Known TP53 mutant glioblastoma (Note: testing is not mandatory for inclusion). * Known Isocitrate dehydrogenase (IDH) mutant grade IV astrocytoma (Note: testing is not mandatory for inclusion). * Patient who must receive or intends to receive restricted medications. * Patients with pacemakers or other metallic implants that can interfere with the magnetic field during Magnetic Resonance Imaging (MRI) investigations. * Inability to undergo contrast-enhanced MRI (Glomerular Filtration Rate (GFR) \<30 mL/min). * Exclusion criteria Part Phase Ia: * Patients who have received previous systemic therapy (with the exception of patients who participated in Phase 0) or radiotherapy for glioblastoma. * Patients who must or intend to continue the intake of restricted medications or any drug considered likely to interfere with the safe conduct of the trial. * Patients with pacemakers or other metallic implants that can interfere with the magnetic field during MRI investigations. * Inability to undergo contrast-enhanced MRI (GFR \<30 mL/min). Further exclusion criteria applies.