This is like asking Bing for proof that there is no god.

You can’t prove that something is not there….

How would that work? Here, see that? It doesn’t exist!

Is it possible to have a profile in Nostr so that messages (DMs and public) need sats attached in order to appear?

But can be skipped if you follow the user sending the message.

This way, friends can message you freely but spammers would have to pay you.