Please stop. You don't know what you're talking about. nostr private messages are not synced by any central server. The protocol doesn't lend itself to having very reliable Private messages. For privacy, on nostr, there are a few ways to DM and not all clients use the private way. If they don't, it's terrible for privacy. If they do, well you better hope it's battle tested and that your recipient is using a client that supports it, and if it does you better hope it's programmed well enough to reply in kind instead of insecurely.