Mo-Rez in First- Line (1L) Maintenance Treatment of Non- Homologous Recombination Deficient Ovarian Cancer (HRd OC) [BEHOLD-Ovarian03]

This study specifically aims to evaluate how well mocertatug rezetecan (Mo-Rez) alone or in combination with bevacizumab works in treating ovarian cancer compared to bevacizumab alone or active observation (AO). The study also assesses whether Mo-Rez is safe and tolerated well by participants in comparison to bevacizumab alone OR AO and will help provide a better understanding of the main side effects of the drugs.

Inclusion Criteria: Participants are eligible to be included in the study only if all of the following criteria apply: * Is at least 18 years of age and the legal age of consent in the jurisdiction in which the study is taking place at the time of signing the Informed Consent Form (ICF). * Has newly diagnosed Stage III/IV (2014 FIGO staging) \[Berek, 2021\] epithelial ovarian, primary peritoneal or fallopian tube cancer with a histologically confirmed diagnosis of high grade serous, high grade endometrioid, clear cell carcinoma, carcinosarcoma or mixed histology. * Has completed first-line platinum-based chemotherapy cycles. Inclusion of IV regimens at Q3W cycles, consolidation regimens and Intravenous (IV)/ Intraperitoneal (IP) and Hyperthermic intraperitoneal chemotherapy (HIPEC) regimens are acceptable. In the event of history of platinum or paclitaxel allergy, alternative agents are allowed (in consultation with the sponsor). At least cycles of first-line chemotherapy must be completed with or without bevacizumab. * Has Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST v1.1) response determined by investigator after the completion of first-line treatment must be Complete response (CR), Partial response (PR), No evidence of disease (NED), or Stable disease (SD). * Is able to commence C1D1 of study treatment within 9 weeks of the final dose of front-line therapy. Final dose of front-line therapy is defined as the last day that platinum-based chemotherapy with/without bevacizumab was given. Participants may continue bevacizumab dosing if specified cycles of bevacizumab post-chemotherapy are administered prior to randomization. * If planning to receive bevacizumab: Has received at least specified number of cycles of bevacizumab per label and local approval in combination front-line chemotherapy * Has provided a sample sufficient for Homologous repair deficiency (HRD) testing (if local testing is not available), and the results available prior to date of randomization. * Tumor specimen should be obtained from the most recent procedure and from a site not previously irradiated. If a suitable archival sample is not available, a fresh tumor tissue sample must be obtained during Screening. Fine needle aspirates, bone marrow samples, bone specimens, or cell blocks are not acceptable. Additional details regarding acceptable biopsy collections and processing can be found in the Laboratory Manual and other laboratory documentation. Tumor sample may also be used for other biomarker testing. * Is willing to use adequate contraception. Contraceptive use should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies. * A female participant is eligible to participate if she is not pregnant or breastfeeding, and 1 of the following conditions applies: * Is a Participant of non-childbearing potential (PONCBP) OR * Is a Participant of childbearing potential (POCBP) and using a contraceptive method that is highly effective (with a failure rate of \1.5 × ULN, provided direct bilirubin is ≤1.5 × ULN and participant otherwise meets entry criteria. * Has cirrhosis or current unstable liver or biliary disease per investigator assessment defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminemia, esophageal/gastric varices, or persistent jaundice. Participants who exhibit these signs or symptoms as a result of the malignancy under investigation and whose conditions are deemed adequately controlled by the investigator may be eligible for inclusion. Stable noncirrhotic chronic liver disease (including Gilbert's syndrome or asymptomatic gallstones), hepatobiliary involvement of malignancy, or chronic stable Hepatitis B virus (HBV) infection (in a participant for whom Hepatitis D virus (HDV) infection has been excluded) or chronic Hepatitis C virus (HCV) infection is acceptable if the participant otherwise meets entry criteria. * Has documented positive Hepatitis B surface antigen (HBsAg) at screening, unless they meet all of the following criteria: * Are receiving effective antiviral therapy (i.e., with nucleos(t)ide analogs with a high barrier to viral resistance \[tenofovir or entecavir\]) for at least 7 days prior to first dose of study intervention and are willing to continue for at least 6 months after the last dose of study intervention or longer at the discretion of the treating hepatologist; * Have undetectable HBV DNA, per institutional or local guidelines, at screening; * Have documented negative HDV antibody testing at screening. * Has documented positive Hepatitis B surface antibody (HBcAb) at screening unless they meet all of the following criteria: * Have undetectable HBV DNA, per institutional or local guidelines, at screening; * Have negative HBsAg at screening. * Has a positive HCV antibody test result at screening unless HCV RNA is negative, indicating past resolved HCV infection, including participants who have undergone curative treatment. The HCV RNA test is optional, and participants with a negative HCV antibody test are not required to undergo HCV RNA testing as well. Participants with a positive HCV antibody test result due to prior resolved disease can be enrolled if a confirmatory negative HCV RNA test is obtained and the participant otherwise meets entry criteria. * Has QTcF \>470 msec. * Has a history within 12 months prior to screening of clinically significant or uncontrolled cardiac disease, acute MI, New York Heart Association Class III or IV congestive heart failure \], or clinically significant arrhythmia not controlled by standard of care therapy. * Has baseline Left ventricular ejection fraction (LVEF) \