I’ve seen a few pop up and I’m not sure there’s much that can be done.

I’ve seen one impersonator that has used two separate npubs that was very nasty and rude about the person they were impersonating and to me.

In your case, I received a DM…nothing bad, just a hey, how are you type DM, thought it was strange and checked the npub.

Maybe try to reach out and ask them to stop. If that doesn’t work, make a post that you have an impersonator so that your followers know and if they don’t get any interactions, they will stop on their on. That’s what I’ve noticed on NOSTR, people that get little to no interaction or are rude and mean seem to find their own fate because no one here (at least that I follow) wants to engage in that behavior.

Wish you the best with this…🤙🏻💜