The purpose of this study is to assess the efficacy and tolerability of rilvegostomig in combination with bevacizumab with or without tremelimumab as first-line treatment in participants with advanced HCC. The study comprises 2 parts - a safety lead-in and a randomised period. Prior to the start of the randomised period of the study, a single-arm safety lead-in period will be applied to evaluate the safety and tolerability of rilvegostomig in combination with bevacizumab and tremelimumab.