Now you can delete chats in Microsoft Teams

Microsoft Teams recently introduced chat delete feature which allows you to delete unwanted chats to reduce clutter. It does not delete it for other chat participants. Chats (like email) may be retained by the compliance team for many years, as per the regulatory requirements.

https://support.microsoft.com/en-us/office/delete-a-chat-in-microsoft-teams-free-ec4bfaa8-2197-4541-8bb4-edbef256f29e