The problem is that iOS doesn't differentiate between a call that merely checks for the presence of a clipboard entry (e.g. so you can enable "Paste" in a menu/submenu) and actually copying the contents of the clipboard.
The workaround (for legitimate apps) is to simply always keep that "Paste" option enabled--even if the clipboard is empty. That way you won't freak out your users and only suffer the most minor of usability consequences.
Having said that I don't think TikTok has any relevant functionality such as enabling a "Paste" option so... Most likely nefarious!
I believe any time you paste with the native keyboard UI up it doesn't go through the app. You only need to snoop the clipboard if you want to proactively use the data without having the user paste.
The workaround (for legitimate apps) is to simply always keep that "Paste" option enabled--even if the clipboard is empty. That way you won't freak out your users and only suffer the most minor of usability consequences.
Having said that I don't think TikTok has any relevant functionality such as enabling a "Paste" option so... Most likely nefarious!