What are the national security concerns as a reason for the TikTok ban? No one is explaining.

What are the national security concerns as a reason for the TikTok ban? No one is explaining.
I have read and listened to many podcasts about national security concerns.

A few millions of people in the US watch videos on TikTok. What to buy, how to cook, funny videos, cat videos, blah blah..

Can someone explain intelligently why watching videos on TikTok is a threat to national security? How is the Chinese government going to use this knowledge of watching videos to harm people in the US?
What is the Chinese government learning from these videos?

All I hear is ban.. ban..ban. WHY?
This appears to me like phobia without clear evidence.