How to delete a personal conversation on both sides?

Nextcloud Talk (spreed)

Not to be confused with group chats or public link chats, I’m referring to one on one direct user conversation. The only option is to “Leave conversation”. How does one DELETE all the messages in that conversation so that they’re nowhere in the database anymore? Is it even possible?

What happens when a user leaves a conversation? What happens when the second user leaves the same conversation? There’s no documentation that answers how nextcloud processes those tasks.