This is a multinational, multicenter, randomized, double-blind, placebo-controlled, Phase 3 induction study to evaluate the efficacy and safety of duvakitug in participants with moderately to severely active Ulcerative Colitis (UC). Study details include: The study duration may be up to 35 weeks with: * Screening period * 12-week Sub-Study 1 (Single-Arm Open-Label Feeder Induction) or Sub-Study 2 (Pivotal Induction) * 12-week Sub-Study 3 (Extended Induction for non-responders) * 45 days follow-up visit for participants who do not enroll into the maintenance study (EFC18359) The treatment duration will be up to 12 weeks in each sub-study. The number of scheduled on-site visits will be up to 8 for the Sub-Study 1 and Sub Study 2 or a maximum of 15 visits for participants completing extended induction.