Testing the Addition of an Anti-cancer Drug, Elimusertib (BAY 1895344) ATR Inhibitor, to the Chemotherapy Treatment (Gemcitabine) for Advanced Pancreatic and Ovarian Cancer, and Advanced Solid Tumors

Inclusion Criteria: * DOSE ESCALATION COHORT: * Patients must have histologically confirmed solid tumor malignancy that is not curable with standard approaches. Gemcitabine must be considered a standard therapy for the participant's malignancy * Patients must have a measurable disease, in at least one lesion, for both the dose escalation and expansion cohorts, as defined by Response Evaluation Criteria in Solid Tumors (RECIST) version (v)1.1 * Patients must have received one line of treatment for their incurable cancer before enrolling in this trial. Patients with rare malignancies for which there is no accepted standard chemotherapy regimen can enroll without any prior treatments * Patients must not have received more than two lines of cytotoxic chemotherapy * Patients can have received prior gemcitabine * Adjuvant chemotherapy is counted as one line of treatment if patients received it within 6 months of their cancer recurring * There is no limit for lines of prior targeted therapies or immunotherapy * Patients who received a prior PARP inhibitor must have had progressive disease, or intolerable toxicity, on the PARP inhibitor prior to enrolling on the study * DOSE EXPANSION COHORT: * Participants must have a histologically confirmed advanced pancreatic adenocarcinoma or ovarian cancer (high grade serous ovarian, primary peritoneal or fallopian tube cancer) that is not curable with standard approaches. Patients with both metastatic pancreatic cancer and unresectab…