It’s not an actual national security issue like selling China nukes or something.
While I agree with your stance that this is infringing on personal freedoms of American citizens, and I too wish our leaders wouldn't always so eagerly infringe on personal freedoms in the name of national security, the national security claim itself does have merit.
I think the notion that WeChat is a threat to national security is honestly ridiculous. National security is a legal excuse to do things Trump otherwise wouldn’t be able to do in his pursuit of a trade war.
Again, not condoning the restriction of personal freedoms, but the national security angle is not totally without merit.
While people like you whine about your chat app, it can be a matter of life and death if China is allowed to continue.