This study is looking at two medicines, **remibrutinib** and **dupilumab**, for adults with *Chronic Spontaneous Urticaria (CSU)*, a condition causing itchy hives not controlled by *H1-antihistamines*, a common allergy medicine. The study has different parts: a screening period lasting up to 4 weeks, a 12-week treatment period, and an optional 12-week follow-up. During the treatment, participants will take either remibrutinib pills or dupilumab shots, along with their usual H1-antihistamines. **Key Points:** - The **study lasts up to 24 weeks**, including treatment and follow-up. - Participants will need to take medicines **daily and visit the study center regularly**. - There are **screening** and **eligibility requirements**, including age and previous treatments. Participants should not have used remibrutinib or dupilumab before and must be able to keep a daily diary of symptoms. The study checks if these treatments help when H1-antihistamines alone don't work. Participants will be monitored for safety, and if the study medicine becomes available commercially, they may continue using it.