It's conceivable that your account status or device settings prevent you from favoriting videos on TikTok if you're experiencing problems using that feature. You might not be able to favorite videos on TikTok for the following reasons:
Account status: If you have a new TikTok account or have violated TikTok's community guidelines, you may not be able to favorite videos. TikTok may restrict certain features until your account has been active for a certain period of time or until your account has been reviewed and approved.
Device settings: TikTok requires certain permissions to be enabled on your device in order to use all of its features. If you have disabled the "Storage" permission on your device, you may not be able to favorite videos. Make sure that you have enabled all necessary permissions in your device settings.
Technical issues: Sometimes, technical issues with the TikTok app can prevent you from being able to favorite videos. Try restarting the app or your device, or updating the app to the latest version to see if this resolves the issue.
If none of these solutions work, you may need to contact TikTok support for further assistance.