The app looks poorly made and there are clear spelling mistakes plus the fact that it was not offered by TikTok which should have made you suspicious. It sucks this happened but maybe you should have done some research and checked if this app actually did belong to TikTok. I assume the app also asked you to login to Facebook directly rather than OAuth which should also made you suspicious.
I find it hard to believe this was a Social Engineering based attack. Elon Musk’s account was accessed multiple times after their tweets being deleted and it seemed to last forever, account by account being taken over.