As Tiktok is a 3rd party app, fix needs to be performed from the application side. It would be best if you let app developers know of this issue through their support channels. Some members had success clearing data and cache of the app.
If Samsung keyboard is closing by itself, Please update Samsung members app to latest version from galaxy store and send us an error report immediately after experiencing the issue from the Samsung member’s app -> Beta Feedback -> Error Reports to help us debug the issue. We apologize for the inconvenience and appreciate your contribution to the beta program.
One UI Beta Team