Aye, here is a handy link (https://l5r.fandom.com/wiki/Topaz_Champion) to know what contest entails. Basically it's rokugan youths rite of passage to participate, at least once, in the competition. Which is open to all as has varied contests. Of course, considering what contest subjects are, mostly minor or great clans had any chance to succeed to get 5 scores of points entering final rounds with  Iaijutsu elimination tournament (I doubt commoners/peasants weren't allowed likely as all fields covered are samurai accepted arts). But would not surprise much if there is festival/fair where commoners run their own contests alongside the Topaz Tournament among themselves.