SYS6043

The goal of this clinical trial is to learn if investigational drug called SYS6043 works in adults with advanced or metastatic solid tumors that have spread or cannot be treated with standard therapies. The main goals of the study are to understand how safe SYS6043 is, what side effects it may cause, and what dose can be given safely. Researchers will also study how the drug moves through the body and whether the immune system reacts to it. In addition, the study will look for early signs that SYS6043 may help slow or shrink tumors and explore whether the amount of a tumor protein called B7-H3 is related to how well the treatment works. Participants will: * Provide written informed consent * Undergo screening tests to ensure they are eligible for study treatment * Attend all required study visits and receive SYS6043 by intravenous infusion once every 3 weeks (Q3W), with 21 days as one treatment cycle until the study doctor determines that study treatment should be stopped based on how well a participant is doing on treatment. * Have safety follow-up (SFU), and long-term follow-up. * Be followed until progression.