This study is testing a new drug called duvakitug for people with Crohn's Disease (CD), a type of bowel disease that causes swelling and irritation in the digestive tract. The study will take up to 35 weeks, which includes a screening period of up to 5 weeks and different sub-studies lasting 12 weeks each, followed by a 6-week follow-up for some participants. A placebo-controlled study means some participants will get a pill with no medicine to compare results. The study is double-blind, so neither participants nor doctors know who receives the actual drug, making results unbiased. The study seeks people aged 18-80 (or 16-18 if they meet specific growth criteria) with moderate to severe CD and who haven't responded well to other treatments. People with other bowel diseases or specific medical conditions are not eligible. Participants may have up to 15 study visits depending on their study group.

• Study lasts up to 35 weeks, with various sub-studies and follow-up.
• Participants must be 18-80 years old and have moderate to severe CD.
• Up to 15 study visits may be required.