RecruitingPhase 2Drug trialEfficacy and Safety of Combined With Immunotherapy After Induction Therapy With Chemotherapy and Targeted Therapy in the First-line Treatment of Microsatellite Stable (MSS) Initially Unresectable Metastatic Colorectal CancerThe goal of this clinical trial is to explore the feasibility of a new mode of chemotherapy and bevacizumab induction therapy combined with immunotherapy as first-line treatment for patients with initially unresectable metastatic colorectal cancer (MSS). The main questions it aims to answer are: 1. To explore the efficacy and safety of this treatment mode 2. Try to study treatment benefit the characteristics of the crowd Participants will combined with immunotherapy after chemotherapy and bevacizumab induction therapy.