When the USA says that its citizens and citizens of other nations using a certain application, device or any other technology is a threat to national security, it does not mean there is an actual threat. What the USA and its agencies mean, is that they don't have surveillance ability on the application, device or whatever the technology.
For example, there is nil threat to the USA from its peopling using Chinese applications or any other Chinese technology. The real complaint the USA has, it can't spy on its citizens and the citizens of other nations through Chinese technology.
The USA and its agencies generally do not have data-sharing agreements with Chinese owned entities, and hence don't have the same access to people's data as they do through USA owned applications and technology.
When the USA does not have control, it perceives it as a threat and will go to any lengths to gain control. This includes extremes from corporate and economic assassination to starting military wars.