The fun part is they don't know the extent of the comprise or how long it has been going on.
What happened is that CISA recently published a report stating that they think a lot of US telecommunications equipment has been compromised. It isn't a one time breach. They know that China has control over a unspecified amount of critical components. The malware China is using is extremely complex and very hard if not completely impossible to detect. China is very good at covering there tracks so even getting a sample of Malware is hard.
Because of all this, CISA is now recommending that people use encrypted messagers.
How much of this was delivered through the TikTok app?
None. It was built into the hardware. TikTok isn't telecommunications related
This was caused by lowest bidder decision making. Along with a tolerance for critical systems designed, developed and manufactured outside of North America and Western Europe. If a country doesn’t have a history of liberal democracy, they can never be fully trusted.
I think trust is the problem honesty trust less and you won't have to worry as much.