This clinical trial is studying Primary Progressive Multiple Sclerosis (PPMS), a form of multiple sclerosis that slowly gets worse over time. The treatment being tested is orelabrutinib, an oral tablet taken by mouth, and it is being compared with placebo tablets that look the same. The purpose of the study is to see whether orelabrutinib can help delay disability getting worse in people with PPMS.

People in the study are assigned by chance to receive either orelabrutinib or placebo. The study is set up so that neither the participants nor the study doctors know which treatment is being given during the trial. Treatment is taken over time, and the study follows participants to see how their condition changes during the study period.

PPMS can affect walking, balance, hand use, and other body functions. Disability progression means a gradual increase in these problems. The study is designed to compare how often this worsening happens in the two groups.