This study is researching an experimental drug called ubamatamab, also referred to as "study drug". The study is focused on patients who have advanced ovarian cancer. The aim of the study is to see how safe, tolerable, and effective the study drug is on its own and in combination with other anti-cancer drugs (bevacizumab, cemiplimab, fianlimab and a standard chemotherapy drug, pegylated liposomal doxorubicin \[PLD\]), referred to as "combination drugs'. The study is looking at several other research questions, including: * What side effects may happen from taking the study drug and its experimental combinations * How much study drug and fianlimab is in the blood at different times * Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects) and its combinations