New User identification

Is there any way we can identify new users on WhatsApp?

We are using profile.firstTime in the welcome flow but if user say something instead of Hi or Hello, we are not able to capture that user.

Are you storing the user in the DB also?
If yes, then use DB search on their mobile numbers and if that number exist trigger to another flow and it that number does not exist then store in the DB and trigger another journey for that new user.