This clinical trial is focused on studying the treatment of Chronic Rhinosinusitis (CRS) in adults. CRS is a condition where the sinuses, which are air-filled spaces in the face, become inflamed and swollen for a long time, leading to symptoms like nasal blockage, facial pain, and nasal discharge. The study will evaluate a treatment called the LYR-210 System, which is a powder for inhalation containing the active substance Mometasone Furoate. This treatment is compared to a sham procedure, which is a fake treatment used for comparison purposes.

The purpose of the study is to assess how effective the LYR-210 System is in improving the main symptoms of CRS in participants who do not have nasal polyps and have not responded well to previous medical treatments. Participants will receive the treatment through intranasal use, meaning it is administered through the nose. The study will last for about 24 weeks, during which the changes in symptoms will be monitored and compared to the initial state before the treatment started.

Another medication involved in the study is Dexamethasone, which is a tablet form of a chemical substance used in various treatments. However, the main focus of this trial is on the LYR-210 System. Participants will be monitored for any changes in their symptoms and overall health to determine the safety and effectiveness of the treatment. The study aims to provide valuable information on whether the LYR-210 System can be a beneficial treatment option for those suffering from chronic sinusitis.