Single user Chat rename function
When you're in an one-to-one conversation, the edit (pencil) button seems not to be available, therefore the chat cannot be renamed. The only workaround, or mechanism to rename it, seems to be adding more than two participants.
Voted. Here's a related idea: https://microsoftteams.uservoice.com/forums/555103-public/suggestions/41973619-better-support-for-subject-based-chat-threads-r (Title: Better support for "subject-based" chat threads (replace more email communications))
I'd like to rename 1-to-1 chats based on topic, but I think they always go as one ongoing chat, which is why I suspect it isn't an option
...you're always talking to that single person, so maybe that's why MS doesn't let you rename it? :(