This is a protocol issue. A client could theoretically add it's own encryption or privacy on the sender/receiver/timestamp, but that would only hold for that individual client.
Users on other clients still wouldn't be able to receive the unencrypted DM metadata unless it their client somehow knew how to decrypt it. The other option of just not displaying the metadata doesn't work because other clients would still display it.
Damus has allowed you to see someone else’s pubkey for a while now. Having a single client implement encrypted sent and received timestamps isn’t the answer, you would need a NIP. Nostr is completely public so there’s no good way to send encrypted DMs on a public relay because others could check when the message appeared on the relay. The best option IMO is to just use a private relay for a private conversation. Companies could have their own relays just like they have their own Slack channels.
