This study tests whether adding becotatug vedotin (EGFR-ADC) to standard chemotherapy plus immunotherapy improves outcomes compared to chemotherapy plus immunotherapy alone as first-line treatment for patients with advanced or metastatic biliary tract cancer whose tumors carry EGFR mutations. Participants will be randomly assigned to receive either the experimental combination (becotatug vedotin + pucotenlimab + gemcitabine + cisplatin) or the control combination (pucotenlimab + gemcitabine + cisplatin). The main goal is to see if the experimental group has a higher objective response rate (tumor shrinkage rate). This is a randomized, controlled, open-label, multicenter study led by Sir Run Run Shaw Hospital, Zhejiang University, with Dr. Chen Mingyu as the principal investigator.