Here's how:
1. You need to install Good Lock and the MultiStar module on your Galaxy Z Flip5. (If you live in a region that doesn't support Good Lock, use Fine Lock)

2. Once you have them installed, open Good Lock and go to MultiStar.

3. Tap I ❤️ Galaxy Foldable.

4. Select Launcher Widget.

5. Here, you can tap Enable Launcher Widget and select TikTok and other apps you want to open on the cover screen.

6. On the cover screen, unlock the Galaxy Z Flip5 , and swipe left until you get to the Good Lock launcher to open TikTok.