They ban American companies from distributing or maintaining the application, not specific content. More of a "criminal conspiracy" type of behavior rather than something that would relate to wikileaks or whoever. Can as well argue what is being banned is the data-collection side of the operation since it's the part that depends on using the app. Those companies still have the freedom to publicly state whatever the CCP has to say.

The law indeed needed to be carefully written to "skirt" any first amendment violations, and SCOTUS unanimously agreed it had done so successfully.