This study is being conducted to determine how well participants with stage IV or advanced stage IIIB/C nonsquamous non-small cell lung cancer (NSCLC), that has certain biomarkers (negative for PD-L1, and positive for KRAS p.G12C) respond to treatment with chemotherapy (carboplatin and pemetrexed) combined with either sotorasib or pembrolizumab. The study will determine whether sotorasib and chemotherapy reduces the risk of your cancer getting worse and improves your survival (i.e. increases the chance of you living longer) compared to the current standard treatment with pembrolizumab and chemotherapy. In this study, participants will be screened and if they meet criteria will be enrolled into the main study and assigned, by chance, into one of 2 groups. You will have an equal chance of taking sotorasib platinum doublet combination chemotherapy or pembrolizumab platinum doublet combination chemotherapy. It is hoped that the information gained from the study will help refine future chemotherapy programs.