Study Overview: This study looks at a new treatment called IBI343 combined with chemotherapy for patients with advanced pancreatic cancer. It's divided into two phases: Phase Ib, which tests the safety and tolerability, and Phase II, which tests how well the treatment works. In the first phase, doses are adjusted based on safety observations. The second phase involves more participants to confirm the effectiveness of the treatment. Key Points: - **Duration and Visits:** The study involves multiple cycles of treatment, with each cycle lasting three weeks. Participants may receive up to 8 cycles of one of the drugs (oxaliplatin). - **Risks and Safety:** The study carefully monitors for any side effects, adjusting doses if needed to ensure safety. - **Eligibility:** Participants need to have advanced pancreatic cancer that tests positive for a specific marker (CLDN18.2) and have previously undergone a specific kind of chemotherapy. Participants will continue treatment until they either cannot tolerate it, their disease gets worse, or they choose to stop. Regular check-ups are done to monitor the progress and any side effects.