Then they use Google Chrome and hit a phishing-hole site and get their phone owned. But don't worry, they weren't allowed to install Netflix!
The problem here is open-source intelligence because TikTok is very popular among young members who spend all their free time in their bunk on their phone. Limiting the apps might help with that, but I'm highly skeptical. There's already plenty of restrictions on social media use for armed-forces members. I believe that path is the way to go - create restrictions on posting personal information.
Having some paper pusher unit pre-approving millions of potential apps sounds like a giant waste of time. It makes a lot more sense to react to bad stuff (like one-off reactions for a massively popular video sharing app with sketchy Chinese ownership) than pre-emptively ban everything, simply because it won't do much for security beyond what Apple and Google are already doing in the app store.