The most obvious sign that you have been cloned is if a friend reaches out to you to ask if you made a new account. This means someone made a mirror copy of your current account and is reaching out to your friends.
If you have security-savvy friends, they’d probably suspect something fishy is going on right off the bat. Others would add the cloned account but then suspect something’s amiss when the scammer sends a message because the message doesn’t sound like something you’d write.
A few of them might get fooled by these scammers’ tricks. Especially if the latter have spent time studying how you communicate so they can mimic how you write your messages.
To check if there’s a cloned account out there, you can type your name on Facebook search. You can also do this on search engines to check what else is out there.