Thanks for the explanation. To be honest, I haven't thought much about it yet. Is there really no way to encrypt DMs yet? I just stumbled upon a NIP from last year.
Discussion
If I'm not mistaken DM's are already encrypted, but all relays can see which npubs are DMing other npubs. That part it clear, unencrypted data
There are methods (like what I mentioned above) which improve private DM's (NIP-96, Outbox model, etc.) But main issue is still as a relay operator, I can see who you are DMing, at what time, what size of the contents in that message, etc.
Just can't see actual content.