The content of DM’s can not be read by others but the fact that messages are going back and forward is visible by other network participants.

An easy way to make DM’s less visible is to:

Spin up a new key pair , just for this one conversation.

Then share that public key with the npub that you wish to converse with. Lastly the receiving client should then take that key and also spin up and share a separate key pair and start sending messages over this different key-pair then the one you publicly use to post with.

This way a new key pair for both participant in the conversation is spun up , just for this conversation.

That way, the keys can never be linked to public messages that could potentially DOXX the sender.