A Study to Assess the Efficacy and Safety of Induction Therapy With Afimkibart (Also Known as RO7790121) in Participants With Moderately to Severely Active Ulcerative Colitis

Who May Qualify: - Confirmed diagnosis of UC - Moderately to severely active UC assessed by mMS - Bodyweight \>= 40 kilogram (kg) - Up to date with colorectal cancer (CRC) screening performed according to local standards - Demonstrated inadequate response, loss of response and/or intolerance to at least one protocol-specified conventional or advanced UC therapy - Males and females of childbearing potential must meet protocol criteria for contraception requirements Who Should NOT Join This Trial: - Currently known complications of UC (e.g. fulminant colitis, toxic megacolon) - Current diagnosis of Crohn's disease (CD) or indeterminate colitis, microscopic colitis, ischemic colitis, infectious colitis, radiation colitis - Presence of an ostomy or ileoanal pouch - Current diagnosis or suspicion of primary sclerosing cholangitis - Pregnancy or breastfeeding, or intention of becoming pregnant during the study - Past or current evidence of definite low-grade or high-grade colonic dysplasia or adenomas or neoplasia not completely removed - History of malignancy within 5 years, with the exception of malignancies adequately treated with resection for non-metastatic basal cell or squamous cell cancer or in situ cervical cancer - Evidence of infection with Clostridioides difficile (C. difficile; formerly known as Clostridium difficile), cytomegalovirus (CMV), human weakened immune system virus (HIV), Hepatitis B (HBV), Hepatitis C (HCV) - Has evidence of active tuberculosis (TB), latent TB not successfully treated (per local guidance) or inadequately treated TB - Has received protocol-specified prohibited medicines, including known exposure to any type of anti-TL1A therapy Always talk to your doctor about whether this trial is right for you.