Comments & messages

Good morning, seeing a lot of posts about comments/messages and wondering if I have missed something. Can anyone confirm, comments are related to collections or records only and cannot be used to simply message another user?

All of our data is to be seen by the record owner and admin only, so in effect all other users are invisible as they wouldn’t be able to access any other users record.

Is that correct, so userA cannot send a general message to userB and start a conversation between themselves. These conversations would be completely independent of any record or collection.