Hi erm__,
There are a few things you can confirm in order to isolate this issue to Tik Tok itself. Be sure there are no updates available for the app. App updates contain bug fixes and help with feature compatibility so you'll want to make sure that any that may be available have been installed.
Check out the steps to manually update your apps here: How to manually update apps on your Apple device - Apple Support
1. Open the App Store.
2. Tap your profile icon at the top of the screen.
3. Scroll to see pending updates and release notes. Tap Update next to an app to update only that app, or tap Update All.
You can also confirm that your iOS is up to date since not being up to date can cause unexpected issues. Check out: Update your iPhone or iPad - Apple Support
If up to date you may want to reach out to the app developer for further assistance since TikTok is a third-party app. You can find the steps to do so here: How to contact an app developer - Apple Support.
Have a good one!