According to the law the operator of any "website, application, program, or software" that "connects users in a manner that allows users to socially interact with other users on the digital service" and that does not make "commercially reasonable efforts to prevent or mitigate the exposure of minors to harmful material". So that covers all Nostr client, relay and blossom server operators It doesn't matter where in the US or the world the operator is based. If in another country and the court in Mississippi finds the person in violation then that person will have fun on their next visit to the US.